At Swansea University we recently published research, undertaken as part of my PhD, which highlighted the increased use of health services associated with being obese during pregnancy, and the cost of this to the NHS. With a growing interest in the benefits of physical activity, we conducted a further study to assess the impact of physical activity and body mass index (BMI) during pregnancy. We looked at the effects of these on the type of birth a woman has (natural childbirth vs. a need for medical intervention) and the health of the baby (size at birth, length of pregnancy, and health scores at birth).
Extensive research has shown the negative health effects of being overweight during pregnancy. For example, this is associated with an increased risk of developing pre-eclampsia and gestational diabetes. There is an increasing likelihood of needing a caesarean, forceps or a vacuum delivery. There are also negative effects on the health of the baby; being overweight during pregnancy is associated with unhealthily high birth weights (a term known as macrosomia) and low Apgar scores (a method used to assess the health of a child immediately after birth).
Currently, however, studies which report such negative effects have not considered the role of physical activity during pregnancy on birth type. Physical activity is an important factor which can help avoid excessive weight gain during pregnancy. Anecdotal evidence has also suggested that it could lessen the need for medical interventions at birth. To add to this, despite clear recommendations encouraging pregnant women to exercise, some women view pregnancy as a barrier to physical activity, uncertain of the effects on their bodies or the unborn baby. If research could demonstrate beneficial effects of physical activity on birth type and/or infant outcomes, women may be more inclined to continue being active throughout pregnancy.
- Physical activity levels (measured over seven days using an accelerometer, which measures duration and intensity of physical activity);
- Body Mass Index (BMI, collected from antenatal notes);
- Several confounding factors (characteristics that could distort the relationship between physical activity and other outcomes), including age, ethnicity, the number of previous pregnancies, and whether or not they smoked (from questionnaire data and antenatal notes).
Data on delivery and infant outcomes were also gathered for these women, using the Secure Anonymised Information Linkage (SAIL) databank held at Swansea University. These included:
- Whether the woman was induced;
- Mode of delivery (vaginal, assisted with ventouse or forceps, elective or emergency caesarean section);
- The length of each labour stage;
- Duration of hospital stay following the birth;
- If the infant was small for gestational age (SGA) or large for gestational age (LGA);
- If the infant had a low Apgar score (less than 7).
Based on their accelerometer scores, women were divided into two groups, ‘low activity’ and ‘high activity’. Our findings revealed that women in the low activity group:
- Were twice as likely to have a birth assisted by ventouse or forceps, compared to women with high activity levels (26% compared to 13%);
- Had a significantly higher chance of having a caesarean section, compared to women with high activity levels (37% compared to 25%).
However, there were no significant differences in infant outcomes between the high activity and low activity groups.
Importantly, the differences related to delivery were independent of the mother’s weight. Therefore women who were overweight or obese with high activity levels were still more likely to have a normal birth in comparison to women with low activity levels, even if they were a healthy weight.
Due to our study design we can only speculate on the reasons physical activity increased the likelihood of a natural birth. A plausible suggestion offered by other research is that women who are more active during pregnancy are consequently able to cope with the demands of birth through maintained or enhanced fitness. It may also be speculated that women with lower activity levels lead unhealthier lifestyles with regards to diet and weight control. However, at this stage we cannot confirm or negate either possibility.
Our research shows that maternal physical activity may positively affect birth delivery outcomes independent of the mother’s weight. In light of these findings, we should be highlighting the benefits for pregnant women of physical activity itself, not just as a means to lose weight. From an obstetric point of view increasing maternal physical activity levels could lead to a reduction in the number of instrumental and caesarean section deliveries. Future research will look to investigate the effects of maternal activity and weight during pregnancy on offspring size during early infancy.
This piece draws on findings from the following paper:
Morgan K, Rahman M, Hill R, Zhou S, Bijlsma G, Khanom A, Lyons R, Brophy S. ‘Physical activity and excess weight in pregnancy have independent and unique effects on delivery and perinatal outcomes’ PLoS ONE, 9(4):e94532. doi:10.1371/journal.pone.0094532
Reports on this research have also been published by Swansea University and BBC News Wales.
Image sources: Pregnant woman with bike – SimplyBike, via Flickr. Pregnant woman doing yoga – Elsie Escobar, via Flickr.