Metformin Gets a Reproductive Reprieve — For Diabetic Moms and Dads Alike

For decades it’s been thought that preconception use of the oral antidiabetic metformin by mothers and fathers might result in adverse fetal outcomes, including congenital malformations and stillbirths.

Women with type 2 diabetes (T2D) are often advised to switch to insulin before or during early pregnancy out of concern for fetal safety. But two studies from the Harvard T.H. Chan School of Public Health in Boston, Massachusetts — one in mothers, the other in fathers — report that metformin, a common and cost-effective antidiabetic agent, is not associated with a significant increased risk of teratogenicity and negative perinatal outcomes. The studies appear in Annals of Internal Medicine.

The studies may make it easier for physicians to reassure diabetic parents-to-be about the safety of metformin use before conception and in early pregnancy,

In the context of sparse existing safety data, the maternal analysis looked at Medicaid data on 12,489 mothers (mean age, about 30) receiving metformin for pregestational T2D during the period 2000-2018. “Many women become pregnant while still taking noninsulin oral antidiabetics, mostly metformin, and one safety concern is whether metformin could cause birth defects,” lead author Yu-Han Chiu, MD, ScD, an epidemiologist, said in an interview, commenting on the impetus for the study.

“On the one hand, metformin can cross the placenta and might directly affect the fetus. On the other hand, poor blood sugar control is a risk factor for birth defects,” she continued. “Insulin in combination with metformin might control blood sugar better than using insulin alone, which may lower the risk of birth defects.”

Switched to insulin monotherapy or prescribed additional insulin within 90 days of their last menstrual period, mothers were assessed for nonchromosomal fetal malformations and nonlive births, spontaneous abortion, and termination. Continuing metformin or adding insulin to metformin in early pregnancy resulted in little to no increased risk for major malformations in infants.

The estimated risk for nonlive birth was 32.7% with insulin monotherapy and 34.3% with insulin plus metformin polytherapy, for a risk ratio (RR) of 1.02 (95% confidence interval (CI), 1.01-1.04).

In addition, the estimated risk for live birth with congenital malformations was 8.0% (5.70-10.2) under insulin monotherapy and 5.7% under insulin plus metformin (95% CI, 4.5-7.3), amounting to a risk ratio of 0.72 (0.51-1.09).

While the results may involve residual confounding by participants’ glycemic control and body mass index, Dr. Chiu said, “Our findings suggest that the current clinical recommendations to switch from metformin to insulin before pregnancy, due to concerns about birth defects, may require reconsideration.”

She noted that previous trials showed adding metformin to insulin in mid-late pregnancy also improved blood sugar control with no increase in risk of birth defects. “However, most of these studies started treatment too late — between 10 and 34 weeks of pregnancy — to determine if metformin could cause birth defects.”

Observational studies found that women with pregestational diabetes who used noninsulin antidiabetics (mainly metformin) in the first trimester had a lower risk of birth defects, compared with those who used insulin, Dr. Chiu added. “However, comparing metformin with insulin may have some biases because women who used metformin generally have less severe diabetes than those who used insulin.”

Aligning with these reassuring findings, a randomized, placebo-controlled trial reported that adding metformin to insulin did not lead to a higher incidence of neonatal morbidity and mortality and was associated with better maternal glycemic control and reduced maternal weight gain. Metformin-exposed offspring, however, had lower birth weights and a higher incidence of being small for gestational age.

Similarly, a recent Nordic register study of more than 3.7 million infants also found no evidence of an increased risk of major defects with the use of metformin vs insulin in the first trimester.

Despite such reassuring findings, however, Dr. Chiu stressed the need to study other pregnancy and infant outcomes as well as the safety of other oral antidiabetics during pregnancy.
 

 

Metformin in Fathers

Turning to fathers, a much larger cohort study by Harvard T.H. Chan investigators looked at the effect of paternal metformin use and also found it to be safe.

The Harvard investigators analyzed diabetic men in 383,851 live births from 1999 to 2020 in an Israeli health fund cohort, excluding those with diabetic spouses. Across different T2D medication groups, paternal age ranged from about 35 to about 43 years. The data revealed that paternal use of metformin monotherapy in the preconception sperm production period was, after adjustment of crude numbers, not associated with major congenital malformations (MCMs) in newborns.

“While metformin has an overall good safety profile, it can lower androgen levels, and there had been some concerns that its use in fathers could alter the sperm, causing adverse effects to the fetus,” lead author and neuroepidemiologist Ran S. Rotem, MD, ScD, of the Harvard School of Public Health, Boston, Massachusetts, said in interview. “Given the increasing prevalence of diabetes in young individuals, more fathers are conceiving a child while using the medication, which could lead to a substantial population effect even if the individual risk is low. But our study suggests that the medication is safe to use by fathers before conception.”

The prevalence of MCMs in the cohort was 4.7% in children of fathers unexposed to diabetes medications (n = 381,041), compared with 6.2% in children of fathers exposed during preconception spermatogenesis to metformin (n = 1730).

By these crude numbers, children with preconception paternal metformin exposure had a nearly 30% increased odds of MCMs. But whereas the crude odds ratio (OR) for MCMs with paternal metformin exposure in all formulations was 1.28 (95% CI, 1.01-1.64), the adjusted OR was 1.00 (95% CI, 0.76 -1.31). Within specific regimens, the adjusted OR was 0.86 (95% CI, 0.60-1.23) for metformin in monotherapy and 1.36 (95% CI, 1.00-1.85) for metformin in polytherapy.

At the outset, Dr. Rotem’s group hypothesized that any crude associations between metformin in polytherapy and birth defects could potentially be explained by poorer underlying parental cardiometabolic risk profiles in those taking multiple diabetes medications. Compared with that of unexposed fathers, the prevalence of cardiometabolic morbidity was indeed substantially higher among both fathers who used metformin during spermatogenesis and their spouses.

In addition, these fathers were more likely to be older, to be smokers, and to have fertility problems. Similarly, mothers were more likely to have cardiovascular comorbidity and to have had fertility problems when the father used metformin.

Moreover, children born to men who used diabetes medications before conception were much more likely to have mothers who also had diabetes and other metabolic conditions, Dr. Rotem noted. “This makes sense since we know that many of these conditions are affected by diet and lifestyle factors that are probably shared across individuals living in the same household.”

Recent research has shown that paternal health and behavior before conception can affect offspring development and long-term health. Characteristics including obesity, diabetes, and metabolic syndrome are seen to affect offspring via complex indirect and direct mechanisms, both genetic and nongenetic.

Doing little to dispel safety concerns, a recent Danish national study reported a link between preconception paternal metformin and major birth defects, particularly genital birth defects in boys. That study, however, lacked data on medication adherence and glycemic control.

“These are well-conducted studies, but it would be useful to see them replicated in different populations, as the sample sizes eligible for analysis are relatively small and some of the confidence intervals are wide,” said Robert W. Platt, PhD, a professor in the departments of Pediatrics and of Epidemiology, Biostatistics, and Occupational Health at McGill University in Montreal, Canada. “However, the results suggest that type 2 diabetics can focus on the most effective treatment pathway for their condition. Metformin does not appear to confer an increased risk of congenital malformations.”

According to an accompanying editorial by Sarah Martins da Silva. MBChB, MD, a reproductive medicine specialist at the University of Dundee in Scotland, the Israeli findings highlight the importance of factoring the sometimes overlooked issue of paternal health into reproductive planning and prenatal care. She stressed that individual risks and benefits should always be carefully considered and results interpreted with caution since such studies lack information on glycemic control. “Nonetheless, these recent analyses suggest that metformin is a safe and effective treatment option for T2D for men and women trying to conceive as well as for managing hyperglycemia in pregnant women in the first trimester,” she wrote and agreed that it may be time to reconsider current prenatal care guidelines that advocate switching to insulin therapy.

The studies by Dr. Chiu and Dr. Rotem were funded by the National Institutes of Health. Dr. Chiu and Dr. Rotem had no competing interests to declare. Dr. Hernandez Diaz, a coauthor on both studies, reported funding from Takeda and consulting for Moderna, Johnson & Johnson, and UCB. Several authors reported support from government and not-for-profit research funding agencies. Dr. Platt disclosed no competing interests. Editorial commentator Dr. Martins da Silva disclosed consulting, speaking, travel, and advisory fees from, variously, Dyneval, Ferring Pharmaceutical, Merck, IBSA, and Gedeon Richer.

For decades it’s been thought that preconception use of the oral antidiabetic metformin by mothers and fathers might result in adverse fetal outcomes, including congenital malformations and stillbirths.

Women with type 2 diabetes (T2D) are often advised to switch to insulin before or during early pregnancy out of concern for fetal safety. But two studies from the Harvard T.H. Chan School of Public Health in Boston, Massachusetts — one in mothers, the other in fathers — report that metformin, a common and cost-effective antidiabetic agent, is not associated with a significant increased risk of teratogenicity and negative perinatal outcomes. The studies appear in Annals of Internal Medicine.

The studies may make it easier for physicians to reassure diabetic parents-to-be about the safety of metformin use before conception and in early pregnancy,

In the context of sparse existing safety data, the maternal analysis looked at Medicaid data on 12,489 mothers (mean age, about 30) receiving metformin for pregestational T2D during the period 2000-2018. “Many women become pregnant while still taking noninsulin oral antidiabetics, mostly metformin, and one safety concern is whether metformin could cause birth defects,” lead author Yu-Han Chiu, MD, ScD, an epidemiologist, said in an interview, commenting on the impetus for the study.

“On the one hand, metformin can cross the placenta and might directly affect the fetus. On the other hand, poor blood sugar control is a risk factor for birth defects,” she continued. “Insulin in combination with metformin might control blood sugar better than using insulin alone, which may lower the risk of birth defects.”

Switched to insulin monotherapy or prescribed additional insulin within 90 days of their last menstrual period, mothers were assessed for nonchromosomal fetal malformations and nonlive births, spontaneous abortion, and termination. Continuing metformin or adding insulin to metformin in early pregnancy resulted in little to no increased risk for major malformations in infants.

The estimated risk for nonlive birth was 32.7% with insulin monotherapy and 34.3% with insulin plus metformin polytherapy, for a risk ratio (RR) of 1.02 (95% confidence interval (CI), 1.01-1.04).

In addition, the estimated risk for live birth with congenital malformations was 8.0% (5.70-10.2) under insulin monotherapy and 5.7% under insulin plus metformin (95% CI, 4.5-7.3), amounting to a risk ratio of 0.72 (0.51-1.09).

While the results may involve residual confounding by participants’ glycemic control and body mass index, Dr. Chiu said, “Our findings suggest that the current clinical recommendations to switch from metformin to insulin before pregnancy, due to concerns about birth defects, may require reconsideration.”

She noted that previous trials showed adding metformin to insulin in mid-late pregnancy also improved blood sugar control with no increase in risk of birth defects. “However, most of these studies started treatment too late — between 10 and 34 weeks of pregnancy — to determine if metformin could cause birth defects.”

Observational studies found that women with pregestational diabetes who used noninsulin antidiabetics (mainly metformin) in the first trimester had a lower risk of birth defects, compared with those who used insulin, Dr. Chiu added. “However, comparing metformin with insulin may have some biases because women who used metformin generally have less severe diabetes than those who used insulin.”

Aligning with these reassuring findings, a randomized, placebo-controlled trial reported that adding metformin to insulin did not lead to a higher incidence of neonatal morbidity and mortality and was associated with better maternal glycemic control and reduced maternal weight gain. Metformin-exposed offspring, however, had lower birth weights and a higher incidence of being small for gestational age.

Similarly, a recent Nordic register study of more than 3.7 million infants also found no evidence of an increased risk of major defects with the use of metformin vs insulin in the first trimester.

Despite such reassuring findings, however, Dr. Chiu stressed the need to study other pregnancy and infant outcomes as well as the safety of other oral antidiabetics during pregnancy.
 

 

Metformin in Fathers

Turning to fathers, a much larger cohort study by Harvard T.H. Chan investigators looked at the effect of paternal metformin use and also found it to be safe.

The Harvard investigators analyzed diabetic men in 383,851 live births from 1999 to 2020 in an Israeli health fund cohort, excluding those with diabetic spouses. Across different T2D medication groups, paternal age ranged from about 35 to about 43 years. The data revealed that paternal use of metformin monotherapy in the preconception sperm production period was, after adjustment of crude numbers, not associated with major congenital malformations (MCMs) in newborns.

“While metformin has an overall good safety profile, it can lower androgen levels, and there had been some concerns that its use in fathers could alter the sperm, causing adverse effects to the fetus,” lead author and neuroepidemiologist Ran S. Rotem, MD, ScD, of the Harvard School of Public Health, Boston, Massachusetts, said in interview. “Given the increasing prevalence of diabetes in young individuals, more fathers are conceiving a child while using the medication, which could lead to a substantial population effect even if the individual risk is low. But our study suggests that the medication is safe to use by fathers before conception.”

The prevalence of MCMs in the cohort was 4.7% in children of fathers unexposed to diabetes medications (n = 381,041), compared with 6.2% in children of fathers exposed during preconception spermatogenesis to metformin (n = 1730).

By these crude numbers, children with preconception paternal metformin exposure had a nearly 30% increased odds of MCMs. But whereas the crude odds ratio (OR) for MCMs with paternal metformin exposure in all formulations was 1.28 (95% CI, 1.01-1.64), the adjusted OR was 1.00 (95% CI, 0.76 -1.31). Within specific regimens, the adjusted OR was 0.86 (95% CI, 0.60-1.23) for metformin in monotherapy and 1.36 (95% CI, 1.00-1.85) for metformin in polytherapy.

At the outset, Dr. Rotem’s group hypothesized that any crude associations between metformin in polytherapy and birth defects could potentially be explained by poorer underlying parental cardiometabolic risk profiles in those taking multiple diabetes medications. Compared with that of unexposed fathers, the prevalence of cardiometabolic morbidity was indeed substantially higher among both fathers who used metformin during spermatogenesis and their spouses.

In addition, these fathers were more likely to be older, to be smokers, and to have fertility problems. Similarly, mothers were more likely to have cardiovascular comorbidity and to have had fertility problems when the father used metformin.

Moreover, children born to men who used diabetes medications before conception were much more likely to have mothers who also had diabetes and other metabolic conditions, Dr. Rotem noted. “This makes sense since we know that many of these conditions are affected by diet and lifestyle factors that are probably shared across individuals living in the same household.”

Recent research has shown that paternal health and behavior before conception can affect offspring development and long-term health. Characteristics including obesity, diabetes, and metabolic syndrome are seen to affect offspring via complex indirect and direct mechanisms, both genetic and nongenetic.

Doing little to dispel safety concerns, a recent Danish national study reported a link between preconception paternal metformin and major birth defects, particularly genital birth defects in boys. That study, however, lacked data on medication adherence and glycemic control.

“These are well-conducted studies, but it would be useful to see them replicated in different populations, as the sample sizes eligible for analysis are relatively small and some of the confidence intervals are wide,” said Robert W. Platt, PhD, a professor in the departments of Pediatrics and of Epidemiology, Biostatistics, and Occupational Health at McGill University in Montreal, Canada. “However, the results suggest that type 2 diabetics can focus on the most effective treatment pathway for their condition. Metformin does not appear to confer an increased risk of congenital malformations.”

According to an accompanying editorial by Sarah Martins da Silva. MBChB, MD, a reproductive medicine specialist at the University of Dundee in Scotland, the Israeli findings highlight the importance of factoring the sometimes overlooked issue of paternal health into reproductive planning and prenatal care. She stressed that individual risks and benefits should always be carefully considered and results interpreted with caution since such studies lack information on glycemic control. “Nonetheless, these recent analyses suggest that metformin is a safe and effective treatment option for T2D for men and women trying to conceive as well as for managing hyperglycemia in pregnant women in the first trimester,” she wrote and agreed that it may be time to reconsider current prenatal care guidelines that advocate switching to insulin therapy.

The studies by Dr. Chiu and Dr. Rotem were funded by the National Institutes of Health. Dr. Chiu and Dr. Rotem had no competing interests to declare. Dr. Hernandez Diaz, a coauthor on both studies, reported funding from Takeda and consulting for Moderna, Johnson & Johnson, and UCB. Several authors reported support from government and not-for-profit research funding agencies. Dr. Platt disclosed no competing interests. Editorial commentator Dr. Martins da Silva disclosed consulting, speaking, travel, and advisory fees from, variously, Dyneval, Ferring Pharmaceutical, Merck, IBSA, and Gedeon Richer.

For decades it’s been thought that preconception use of the oral antidiabetic metformin by mothers and fathers might result in adverse fetal outcomes, including congenital malformations and stillbirths.

Women with type 2 diabetes (T2D) are often advised to switch to insulin before or during early pregnancy out of concern for fetal safety. But two studies from the Harvard T.H. Chan School of Public Health in Boston, Massachusetts — one in mothers, the other in fathers — report that metformin, a common and cost-effective antidiabetic agent, is not associated with a significant increased risk of teratogenicity and negative perinatal outcomes. The studies appear in Annals of Internal Medicine.

The studies may make it easier for physicians to reassure diabetic parents-to-be about the safety of metformin use before conception and in early pregnancy,

In the context of sparse existing safety data, the maternal analysis looked at Medicaid data on 12,489 mothers (mean age, about 30) receiving metformin for pregestational T2D during the period 2000-2018. “Many women become pregnant while still taking noninsulin oral antidiabetics, mostly metformin, and one safety concern is whether metformin could cause birth defects,” lead author Yu-Han Chiu, MD, ScD, an epidemiologist, said in an interview, commenting on the impetus for the study.

“On the one hand, metformin can cross the placenta and might directly affect the fetus. On the other hand, poor blood sugar control is a risk factor for birth defects,” she continued. “Insulin in combination with metformin might control blood sugar better than using insulin alone, which may lower the risk of birth defects.”

Switched to insulin monotherapy or prescribed additional insulin within 90 days of their last menstrual period, mothers were assessed for nonchromosomal fetal malformations and nonlive births, spontaneous abortion, and termination. Continuing metformin or adding insulin to metformin in early pregnancy resulted in little to no increased risk for major malformations in infants.

The estimated risk for nonlive birth was 32.7% with insulin monotherapy and 34.3% with insulin plus metformin polytherapy, for a risk ratio (RR) of 1.02 (95% confidence interval (CI), 1.01-1.04).

In addition, the estimated risk for live birth with congenital malformations was 8.0% (5.70-10.2) under insulin monotherapy and 5.7% under insulin plus metformin (95% CI, 4.5-7.3), amounting to a risk ratio of 0.72 (0.51-1.09).

While the results may involve residual confounding by participants’ glycemic control and body mass index, Dr. Chiu said, “Our findings suggest that the current clinical recommendations to switch from metformin to insulin before pregnancy, due to concerns about birth defects, may require reconsideration.”

She noted that previous trials showed adding metformin to insulin in mid-late pregnancy also improved blood sugar control with no increase in risk of birth defects. “However, most of these studies started treatment too late — between 10 and 34 weeks of pregnancy — to determine if metformin could cause birth defects.”

Observational studies found that women with pregestational diabetes who used noninsulin antidiabetics (mainly metformin) in the first trimester had a lower risk of birth defects, compared with those who used insulin, Dr. Chiu added. “However, comparing metformin with insulin may have some biases because women who used metformin generally have less severe diabetes than those who used insulin.”

Aligning with these reassuring findings, a randomized, placebo-controlled trial reported that adding metformin to insulin did not lead to a higher incidence of neonatal morbidity and mortality and was associated with better maternal glycemic control and reduced maternal weight gain. Metformin-exposed offspring, however, had lower birth weights and a higher incidence of being small for gestational age.

Similarly, a recent Nordic register study of more than 3.7 million infants also found no evidence of an increased risk of major defects with the use of metformin vs insulin in the first trimester.

Despite such reassuring findings, however, Dr. Chiu stressed the need to study other pregnancy and infant outcomes as well as the safety of other oral antidiabetics during pregnancy.
 

 

Metformin in Fathers

Turning to fathers, a much larger cohort study by Harvard T.H. Chan investigators looked at the effect of paternal metformin use and also found it to be safe.

The Harvard investigators analyzed diabetic men in 383,851 live births from 1999 to 2020 in an Israeli health fund cohort, excluding those with diabetic spouses. Across different T2D medication groups, paternal age ranged from about 35 to about 43 years. The data revealed that paternal use of metformin monotherapy in the preconception sperm production period was, after adjustment of crude numbers, not associated with major congenital malformations (MCMs) in newborns.

“While metformin has an overall good safety profile, it can lower androgen levels, and there had been some concerns that its use in fathers could alter the sperm, causing adverse effects to the fetus,” lead author and neuroepidemiologist Ran S. Rotem, MD, ScD, of the Harvard School of Public Health, Boston, Massachusetts, said in interview. “Given the increasing prevalence of diabetes in young individuals, more fathers are conceiving a child while using the medication, which could lead to a substantial population effect even if the individual risk is low. But our study suggests that the medication is safe to use by fathers before conception.”

The prevalence of MCMs in the cohort was 4.7% in children of fathers unexposed to diabetes medications (n = 381,041), compared with 6.2% in children of fathers exposed during preconception spermatogenesis to metformin (n = 1730).

By these crude numbers, children with preconception paternal metformin exposure had a nearly 30% increased odds of MCMs. But whereas the crude odds ratio (OR) for MCMs with paternal metformin exposure in all formulations was 1.28 (95% CI, 1.01-1.64), the adjusted OR was 1.00 (95% CI, 0.76 -1.31). Within specific regimens, the adjusted OR was 0.86 (95% CI, 0.60-1.23) for metformin in monotherapy and 1.36 (95% CI, 1.00-1.85) for metformin in polytherapy.

At the outset, Dr. Rotem’s group hypothesized that any crude associations between metformin in polytherapy and birth defects could potentially be explained by poorer underlying parental cardiometabolic risk profiles in those taking multiple diabetes medications. Compared with that of unexposed fathers, the prevalence of cardiometabolic morbidity was indeed substantially higher among both fathers who used metformin during spermatogenesis and their spouses.

In addition, these fathers were more likely to be older, to be smokers, and to have fertility problems. Similarly, mothers were more likely to have cardiovascular comorbidity and to have had fertility problems when the father used metformin.

Moreover, children born to men who used diabetes medications before conception were much more likely to have mothers who also had diabetes and other metabolic conditions, Dr. Rotem noted. “This makes sense since we know that many of these conditions are affected by diet and lifestyle factors that are probably shared across individuals living in the same household.”

Recent research has shown that paternal health and behavior before conception can affect offspring development and long-term health. Characteristics including obesity, diabetes, and metabolic syndrome are seen to affect offspring via complex indirect and direct mechanisms, both genetic and nongenetic.

Doing little to dispel safety concerns, a recent Danish national study reported a link between preconception paternal metformin and major birth defects, particularly genital birth defects in boys. That study, however, lacked data on medication adherence and glycemic control.

“These are well-conducted studies, but it would be useful to see them replicated in different populations, as the sample sizes eligible for analysis are relatively small and some of the confidence intervals are wide,” said Robert W. Platt, PhD, a professor in the departments of Pediatrics and of Epidemiology, Biostatistics, and Occupational Health at McGill University in Montreal, Canada. “However, the results suggest that type 2 diabetics can focus on the most effective treatment pathway for their condition. Metformin does not appear to confer an increased risk of congenital malformations.”

According to an accompanying editorial by Sarah Martins da Silva. MBChB, MD, a reproductive medicine specialist at the University of Dundee in Scotland, the Israeli findings highlight the importance of factoring the sometimes overlooked issue of paternal health into reproductive planning and prenatal care. She stressed that individual risks and benefits should always be carefully considered and results interpreted with caution since such studies lack information on glycemic control. “Nonetheless, these recent analyses suggest that metformin is a safe and effective treatment option for T2D for men and women trying to conceive as well as for managing hyperglycemia in pregnant women in the first trimester,” she wrote and agreed that it may be time to reconsider current prenatal care guidelines that advocate switching to insulin therapy.

The studies by Dr. Chiu and Dr. Rotem were funded by the National Institutes of Health. Dr. Chiu and Dr. Rotem had no competing interests to declare. Dr. Hernandez Diaz, a coauthor on both studies, reported funding from Takeda and consulting for Moderna, Johnson & Johnson, and UCB. Several authors reported support from government and not-for-profit research funding agencies. Dr. Platt disclosed no competing interests. Editorial commentator Dr. Martins da Silva disclosed consulting, speaking, travel, and advisory fees from, variously, Dyneval, Ferring Pharmaceutical, Merck, IBSA, and Gedeon Richer.