Paternal weight influences baby’s size at birth, study finds

Researchers at the University of São Paulo analyzed data from 89 mother-father-baby triads and concluded that the higher the father’s body mass index, the smaller the baby, and that this can influence the baby’s health far into adulthood.

By Maria Fernanda Ziegler  |  Agência FAPESP – A study in Brazil involving 89 father-mother-baby triads points to an association between paternal overweight and newborn birth weight: the higher the father’s body mass index (BMI, weight divided by height squared), the lower the baby’s birth weight.

An article on the study is published in the International Journal of Obesity. 

The findings reinforce the idea that anthropometric issues are not the sole responsibility of the mother and that the father should also strive to maintain a healthy lifestyle during a partner’s pregnancy.

“There is a great deal of discussion and research regarding the link between fetal development and maternal health, including issues such as overweight before and during pregnancy, but the fact is that the father’s health also has a significant impact on the development of the baby both during pregnancy and after birth. Our study was the first involving Brazilian families to show that the higher the father’s BMI, the lower the baby’s birth weight, evidencing the father’s importance to the baby’s health and development,” said Mariana Rinaldi Carvalho, first author of the article and a researcher at the University of São Paulo’s Ribeirão Preto Medical School (FMRP-USP). She was supported by FAPESP via a PhD scholarship. 

Birth weight is considered a key predictor of health not just in early childhood but for life. A great deal of research has shown that babies born with low (or high) weight run a higher risk of death and of developing non-transmissible diseases later in life, such as type 2 diabetes, cancer and cardiovascular disorders.

The study by researchers at FMRP-USP was a follow-up to a clinical trial that investigated the effect of nutritional counseling intervention on weight gain for 350 overweight pregnant women attending public primary health clinics. The trial was supported by FAPESP.

“Having noticed that most studies involving fetal and neonatal health fail to take the parents’ lifestyle into account, we set out to include paternal anthropometry as a factor affecting fetal development,” said Carvalho’s thesis advisor, Daniela Saes Sartorelli, last author of the study and a professor in the Department of Social Medicine at FMRP-USP.

The group plans to analyze the effect of paternal diet on neonatal anthropometry and adiposity, focusing on consumption of ultra-processed foods and fat quality.

Public health

Maternal overweight is considered a public health problem. Many studies have shown that excessive weight gain during pregnancy is a major short- and long-term health hazard for both mother and baby. In the case of the mother, it heightens the risk of gestational diabetes, hypertension and preeclampsia, often making a cesarean section inevitable. For the baby, it increases the likelihood of low or high birth weight and the risk of obesity and associated disorders such as type 2 diabetes and hypertension at an early age.

While in the case of the mother there is a direct link via the placenta and other cells between obesity and fetal development, paternal overweight can lead to epigenetic alterations (biochemical changes to DNA that reprogram gene expression). According to Carvalho, previous studies involving animals showed that some genes expressed by the father can affect fetoplacental growth.

The fetus can suffer growth restrictions influenced by paternal overweight and fail to realize its genetic growth potential, she explained. Briefly, preconception paternal exposure to environmental stressors such as an unhealthy diet, a sedentary lifestyle and smoking, for example, can lead to metabolic disorders in offspring via epigenetic alterations (read more at: agencia.fapesp.br/44803 and agencia.fapesp.br/22005). 

“We now know that environmental stressors such as overweight can influence the structure and quality of the father’s sperm, altering gene expression and affecting the DNA of his children. This influence relates to epigenetics, the scientific field that studies how environmental stimuli can activate or silence genes,” Carvalho explained.

“The mother’s health is evidently a key factor, and research has shown the importance of a healthy diet during pregnancy, but more attention needs to be paid to paternal overweight in the period prior to conception. Our research findings show that just as maternal nutritional counseling is important, so is the need for a preconception change in paternal habits.” 

The study involving 89 parents and babies also found that the higher the father’s BMI and waist circumference, the smaller the baby’s head circumference at birth. “We didn’t detect any anomalies or malformations, but the correlation is important because head circumference at birth is a key growth parameter. Nevertheless, more research is needed to evaluate the real significance of this finding,” Carvalho said, adding that previous studies of obesity found overweight to influence neonatal bone mineralization. 

“A limitation of this study was lack of access to information on the time these women took to deliver their babies [in cases of vaginal birth]. We know head circumference at birth can be altered temporarily when the baby has spent a long time in the vaginal canal,” she said.

The article “Relationship between paternal excessive weight and neonatal anthropometry in a clinical trial of nutritional counseling for pregnant women with overweight” is at: www.nature.com/articles/s41366-024-01639-8#. 

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