Although many women worry about gaining too much weight during pregnancy, not gaining enough can cause significant problems as well. According to a new study published in the journal PLOS One, low maternal weight gain during pregnancy can increase the risk of death among male fetuses.
The present study further demonstrates the sex differences between male and female fetuses. Explains associate professor and reproductive endocrinologist Kristen Navara of the College of Agricultural and Environmental Sciences at the University of Georgia, “Males have an overall higher risk of miscarriage and preterm birth. In addition, male and female embryos are different metabolically and grow at different rates.”
Previous studies on non-mammals have also found that restricted calorie intake leads to lower rates of male offspring. Few studies have investigated the relationship between calorie intake, weight gain, and birth sex ratios in humans.
Comments Navara, “Thus, it remains unclear whether subtle differences in food intake and weight gain during gestation differentially influence male survival in utero and, if so, when during gestation these influences would be most potent.”
Therefore, for the present study, Navara hypothesized that the ratio of male to female babies born would differ depending on maternal weight gain during pregnancy, with lower levels resulting in both more female births and increased male fetal loss.
The study analyzed data collected from over 68 million births over 23 years to assess the relationship between gestational weight gain and natal sex ratios and the relationship between gestational weight gain and sex ratios of fetal deaths at five gestational ages.
The American College of Obstetricians and Gynecologists (ACOG) currently recommends that underweight women gain between 28 and 40 pounds during pregnancy, normal weight women between 25 and 35 pounds, overweight women between 15 and 25 pounds, and obese women between 11 and 20 pounds.
According to the study, women who gained less than 20 pounds during pregnancy produced a much lower proportion of male offspring than female offspring and a much lower proportion of male offspring compared to women who gain more than 20 pounds.
Comments Navara on the findings:
“The correlation was a near perfect relationship where the proportion of males rose with the number of pounds women gained during gestation. To me, that tight of a relationship indicates that weight gain and the sex ratio at birth are, in fact, directly related and that the relationship isn’t driven by another related variable.”
Additionally, women who gain little weight during pregnancy experienced higher rates of male fetal deaths at six months gestation compared to women who gain high amounts of weight.
As Navara explains, “Fetuses are differentially susceptible to inadequate weight gain during pregnancy and that puts males more at risk at least at certain points of gestation.”
In other words, lower levels of maternal weight gain during pregnancy significantly affect the outcome for male babies compared to female babies.
Based on the results of the study, Navara believes that recommendations for weight gain during pregnancy should vary depending on the sex of the fetus:
“Currently, the recommendations for weight gain in pregnancy are the same whether the fetus is male or female, even though it is well known that they grow at different rates and have different metabolic rates. I think it is important to continue the research to determine whether women carrying boys should actually be eating more than women carrying girls in order to maximize the chances of the fetus’s survival.”
Navaro plans to continue her research on the relationship between weight gain during pregnancy and birth sex ratios by studying whether specific dietary factors influence fetal survival.
Low gestational wight gain skews human sex ratios towards females: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0114304
Low maternal weight gain linked to increased risk of male fetal death: http://www.medicalnewstoday.com/articles/286965.php
UGA study finds low weight gain in pregnant women reduces male fetal survival: http://news.uga.edu/releases/article/low-weight-gain-in-pregnant-women-reduces-male-fetal-survival-1214/
Weight gain during pregnancy: http://www.acog.org/Resources-And-Publications/Committee-Opinions/Committee-on-Obstetric-Practice/Weight-Gain-During-Pregnancy
Maternal Weight Gain During Pregnancy: http://www.freeimages.com/photo/1186279