The overall aim of this dissertation is to explore the association between physical exercise before and during pregnancy and reproductive outcomes such as birth weight, gestational age and mode of delivery. A secondary aim was to describe the women who perform regular exercise before and during pregnancy.
The data used for this study are derived from the Norwegian Mother and Child Cohort study (MoBa) conducted by the Norwegian Institute of Public Health. MoBa is a nationwide pregnancy cohort that aimed to include 100,000 pregnancies by 2008 and was designed to explore the associations between some of the lifestyle variables to which pregnant women and their fetuses are exposed in addition to diseases.
Pregnant women are recruited into the study through a postal invitation two weeks ahead of their routine ultrasound examination at gestational week 17 at their local hospital. Data are obtained from 50 out of 52 maternity units in Norway. The overall participation rate for the present data file is 45%. However the follow-up rate from inclusion to questionnaire 3 is 92%.
Participants receive three questionnaires during pregnancy weeks 17 and 30 (Q1, Q2 and Q3). Q1 and Q3 include items of maternal health and lifestyle behaviors, including exercise participation both before and during pregnancy. Q2 is a Food Frequency Questionnaire. Linkage to the Medical Birth Registry of Norway (MBRN) was also provided. The questionnaires are available at www.fhi.no/morogbarn.
The proportion of women exercising regularly was 46.4% before pregnancy and decreased to 28.0 and 20.4% in weeks 17 and 30, respectively. Walking and bicycling were the most frequently reported activities before and during pregnancy. The prevalence of swimming tended to increase from prepregnancy to week 30. Exercising regularly prepregnancy was highly related to regular exercise in week 17, aOR=18.4 (17.1–19.7) and 30, aOR 4.3 (4.1–4.6). Low gestational weight gain was positively associated with regular exercise in week 30, aOR=1.2 (1.1–1.4), whereas being overweight before pregnancy was inversely associated with regular exercise in week 17, aOR=0.8 (0.7–0.8) and 30, aOR=0.7 (0.6–0.7). Also, women experiencing a multiple pregnancy, pelvic girdle pain, or nausea were less likely to exercise regularly.
Excessive newborn birth weight was observed in 4,033 (10.9%) newborns, 56.1% (n=2,263) of whom were born to multiparous women. An inverse association between regular exercise (at least three times per week) and excessive newborn birth weight in pregnancy weeks 17 and 30 was observed in nulliparous women, aOR 0.72 (95% CI 0.56-0.93) and aOR 0.77 (95% CI 0.61-0.96), respectively. Regular exercise performed before pregnancy did not affect the probability of delivering newborns with an excessive birth weight in nulliparous or multiparous women.