Maternal exercise shapes early yolk sac growth, varies with baby’s sex

In a longitudinal study published in Scientific Reports, researchers investigate the effect of maternal physical activity on the scale and growth of the yolk sac during early pregnancy. To this end, maternal physical activity was found to affect human yolk sac development, with this effect depending on gestational age and embryonic sex.

Study: Maternal physical activity affects yolk sac size and growth in early pregnancy, but girls and boys use different strategies. Image Credit: Pixel-Shot / Shutterstock.com

Background

The yolk sac is a structure observed through the early development of the human embryo that gives nutrients and allows gas exchange to the fetus until the placenta develops fully. Furthermore, the yolk sac also plays a job in overall developmental processes akin to protein synthesis, gastrointestinal tract formation, stem cell production, and hematopoiesis.

Various maternal aspects akin to height, weight gain, and sleep duration are known to affect yolk sac size. Maternal physical activity, for instance, is a modifiable lifestyle factor related to glucose control, weight gain, and overall outcomes for the mother and the fetus.

Concerning the study

The current study aimed to grasp how maternal physical activity potentially affects the intrauterine environment and early embryonic development, as indicated by the scale and growth of the yolk sac.

As a component of the continued conception-implantation interval in pregnancy (CONIMPREG) research program, this prospective and longitudinal study included 196 healthy and nonsmoking women with regular menstrual cycles who could conceive naturally. The ladies were between 20 and 35 years old, and their body mass index (BMI) was between 18 and 30 kg/m².

The assessment of participants was conducted at 4 study visits. In the course of the first visit, prior to conception, height and body composition were measured, and physical activity was recorded using an actigraph, a wireless and noninvasive monitor.

Within the second visit at seven weeks of gestation, embryo viability, gestation length, and yolk sac were assessed through ultrasound imaging. At 10 weeks, yolk sac measures were repeated. In the course of the final visit at 13 weeks, maternal physical activity and body composition were reevaluated.

The statistical evaluation involved using peculiar least square linear (OLS) regression models, evaluation of variance (ANOVA), and the estimation of means, standard deviations, minima, and maxima.

Study findings

The mean gestational length was 281 days in line with the last menstrual period (LMP) date or 278.5 days, as reflected by the crown-rump length (CRL) of the embryo in the primary trimester. The pregnancies showed a lower rate of complications, including preterm birth, gestational diabetes, a five-min Apgar rating of seven or less, and gestational hypertension at 3.2%, 3.7%, 1.1%, and three.2%, respectively.

The full activity duration was five hours and 55 minutes prior to conception, which was reduced by one hour and 36 minutes by the tip of the primary trimester. This pattern was consistent between light and moderate-vigorous activity.

The mean yolk sac size was found to be 4.7 mm at week seven, which significantly increased to five.9 mm at week 10 with individual variability. The reproducibility of the ultrasound measurements of the yolk sac size was assessed by measuring the intra- and interobserver variabilities, which were 0.08% and 0.09%, respectively, thus confirming the measurement precision.

When gestational and embryonic age weren’t considered, the yolk sac size was not significantly affected by maternal physical activity. Nonetheless, at week seven of gestation, an increased preconception physical activity was related to a bigger yolk sac diameter in male embryos, with no such effect on female embryos.

At week 10, each embryonic sexes were affected by maternal physical activity. While male embryos showed a negative association between yolk sac size and maternal physical activity at this stage, female embryos showed a robust positive correlation within the two variables, with a 24% larger yolk sac than male embryos.

A big interaction was also observed between embryonic sex and the day by day physical activity of the mother. The consequences at 13 weeks of gestation weren’t statistically significant. Moreover, preconception maternal physical activity was related to variations in yolk sac growth velocity, with a major difference observed among the many two embryonic sexes.

The study’s findings are strengthened by its prospective design, the inclusion of preconception data of healthy women with natural and low-risk pregnancies, and the statistical models used for evaluation. Notable limitations of the study include its relatively low generalizability, in addition to the shortage of continuous measurement of physical activity and control of the impact of maternal nutrition and stress.

Conclusions

The findings reiterate that maternal cues may influence human embryonic growth and development. Maternal physical activity was found to affect yolk sac size in a graded and embryonic sex-specific manner.

During early pregnancy, this effect was found to be briefly phases. Further research is warranted on this area to grasp the impact of maternal physical activity on the offspring’s long-term health.