Prenatal stress increases birth complications and decreases male births

According to a new study published this week, mothers who undergo physical and mental stress during their pregnancies are more likely to deliver prematurely and have birth complications. The study titled, “Maternal prenatal stress phenotypes associate with fetal neurodevelopment and birth outcomes,” was published in the latest issue of the PNAS (Proceedings of National Academy of Sciences of the United States of America).

Image Credit: Zetar Infinity / Shutterstock
Image Credit: Zetar Infinity / Shutterstock

Lead author of the study Catherine Monk, director of women's mental health in OB/GYN at NewYork-Presbyterian/Columbia University Irving Medical Center called the mother’s womb, the baby’s “influential first home” explaining her study. The authors explained that there have been “no studies of which we are aware have considered multiple indicators of maternal stress to identify the types of maternal stress that most influence developing offspring.”

Their study found that maternal stress is also less likely to result in male births. She added, “We do know that males are more vulnerable in utero, and presumably the stress in these women is of a long-standing nature.” She explained that there is an average of 105 boy babies born in comparison to 100 girls. This is natural selection she said because males are more likely to die from physical pursuits. This study reveals that mothers who are physically and mentally stressed during pregnancy or before give birth to less number of boys compared to healthy women. These pregnancies were all healthy, Monk said.

According to her, “Other researchers have seen this pattern of a decrease in male births related to traumatic cataclysmic events. One of them being President Kennedy's assassination and the other being the September 11 terrorist attacks in New York City.”
Physical stress on the mother during and before pregnancy also led to more number of preterm births compared to mothers with low physical stress. Psychological stress too led to longer labour duration and birth complications compared to mothers who were less mentally stressed, the authors of the study wrote.

The team included 27 variables for their study and looked at questionnaires, diaries and physical assessment records of the mothers with single pregnancies. They included 187 mothers in their study. Results showed that 66.8 percent of the mothers were in the healthy group (HG), 17.1 percent belonged to the psychologically stressed group (PSYG) with stress, depression or anxiety and 16 percent belonged to the physically stressed group (PHSG). The PHSG had high calorie intake and high blood pressure. Results showed that if the normal male to female ratio was 105:100, the values were23:18 in HG, 2:3 in the PSYG and 4:9 in the PHSG. Further PHSG babies were born an average of 1.5 weeks earlier than HG babies with 22 percent preterm births (compared to 5 percent in HG). These babies also had lower heart rates at birth. PSYG babies had more birth complications.

Monk said that these factors were reversible. She added that when these expectant mothers were provided social support, there was a lowering of risk of preterm delivery. She said that this came as a surprise and what was more surprising was that more a woman was supported, more the likelihood of her having a boy baby. She said, “The support could be from family and friends. It could be a sense of belonging in a religious community. It's the sense of social cohesion and social connectedness which research suggests is a buffer against the experiences of stress. It means you take a break from it.”

The researchers wrote that there is evidence that one in three pregnant women report psychological stress that arises out of mental ailments such as depression and anxiety or job related strain. The team explains that each of these conditions might be releasing the stress hormone cortisol. This level is meant to combat short durations of stress but chronically raised cortisol could raise the risk of high blood pressure and diabetes in the mother and make her more prone to physical ailments. This could be detrimental for the babies as well, explained the researchers.

The authors of the study write in conclusion, “This study’s key contributions include the use of a data-driven procedure to specify types of maternal stress—psychological and subclinical physical health indicators—that predict offspring outcomes including sex at birth, risk of preterm birth, and fetal neurodevelopment. Social support is a key factor differentiating the stress groups and a malleable intervention target to improve offspring outcomes.”

Monk said that the way get around this would be to reduce physical and mental stress during pregnancy and this could begin at the start of pre natal care. She said, “Why not check in and ask yourself, how are you managing stress? Do you have tools? Do you need some more help? Where's the extra help going to come from? I think it's an ideal time to do that.”

Journal reference:

Maternal prenatal stress phenotypes associate with fetal neurodevelopment and birth outcomes Kate Walsh, Clare A. McCormack, Rachel Webster, Anita Pinto, Seonjoo Lee, Tianshu Feng, H. Sloan Krakovsky, Sinclaire M. O’Grady, Benjamin Tycko, Frances A. Champagne, Elizabeth A. Werner, Grace Liu, Catherine Monk Proceedings of the National Academy of Sciences Oct 2019, 201905890; DOI: 10.1073/pnas.1905890116,

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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