Adapted from BMJ 22nd November 2025
After observing the pregnancies and outcomes of 1.6 million it is best to be in the normal weight range if you can, before becoming pregnant.
The researchers found that 6% of women were underweight, 53% had normal weight, 19% were overweight and 22% had obesity.
Babies born to women who gained too little weight in pregnancy tended to have lower birth weight, have lower chances of caesarean delivery, large for gestational weight babies, macrosomia, higher rates of pre-term birth, small for gestational age infants, low birth weight and respiratory distress.
Gestational weight gain above recommended levels tended to result in higher birth weight, higher rates of caesarean delivery, hypertensive disorders of pregnancy, large for gestational age infants, macrosomia, neonatal intensive care admission, lower rates of pre-term birth and small for gestational age infants.
Observational studies suggest that a higher pre-pregnancy body mass index has a greater impact on pregnancy outcomes and childhood weight than gestational weight gain. Studies of siblings show that maternal obesity at the onset of pregnancy, excessive gestational weight gain and short interpregnancy intervals are all independently associated with obesity in the offspring. Maternal and child health are deeply intertwined across the life course.
Currently about 40% of pregnancies are unplanned, so not all women are open to optimising their weight before pregnancy starts. The Healthy Life Trajectories Initiative and Healthy Adaptation to Pregnancy, Postpartum and Parenthood system aim to improve matters before and between pregnancies.
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