RT Journal Article
SR Electronic
T1 Uterine distention as a factor in birth timing: retrospective nationwide cohort study in Sweden
JF BMJ Open
JO BMJ Open
FD British Medical Journal Publishing Group
SP e022929
DO 10.1136/bmjopen-2018-022929
VO 8
IS 10
A1 Jonas Bacelis
A1 Julius Juodakis
A1 Kristina M Adams Waldorf
A1 Verena Sengpiel
A1 Louis J Muglia
A1 Ge Zhang
A1 Bo Jacobsson
YR 2018
UL http://bmjopen.bmj.com/content/8/10/e022929.abstract
AB Objectives To determine whether uterine distention is associated with human pregnancy duration in a non-invasive observational setting.Design Retrospective cohort study modelling uterine distention by interaction between maternal height and uterine load.Setting The study is based on the 1990–2013 population data from all delivery units in Sweden.Participants Uncomplicated first pregnancies of healthy Nordic-born mothers with spontaneous onset of labour. Pregnancies were classified as twin (n=2846) or singleton (n=527 868). Singleton pregnancies were further classified as carrying a large for gestational age fetus (LGA, n=24 286) or small for gestational age fetus (SGA, n=33 780).Outcome measures Statistical interaction between maternal height and uterine load categories (twin vs singleton pregnancies, and LGA vs SGA singleton pregnancies), where the outcome is pregnancy duration.Results In all models, statistically significant interaction was found. Mothers carrying twins had 2.9 times larger positive linear effect of maternal height on gestational age than mothers carrying singletons (interaction p=5e−14). Similarly, the effect of maternal height was strongly modulated by the fetal growth rate in singleton pregnancies: the effect size of maternal height on gestational age in LGA pregnancies was 2.1 times larger than that in SGA pregnancies (interaction p<1e−11). Preterm birth OR was 1.4 when the mother was short, and 2.8 when the fetus was extremely large for its gestational age; however, when both risk factors were present together, the OR for preterm birth was larger than expected, 10.2 (interaction p<0.0005).Conclusions Across all classes, maternal height was significantly associated with child’s gestational age at birth. Interestingly, in short-statured women with large uterine load (twins, LGA), spontaneous delivery occurred much earlier than expected. The interaction between maternal height, uterine load size and gestational age at birth strongly suggests the effect of uterine distention imposed by fetal growth on birth timing.