Mothers will be recruited at around 12 weeks’ gestation and then sampled (blood, urine, faeces and vaginal fluid) throughout pregnancy (6 times) at approximately 4-week intervals. Sampling times have been selected to coincide with regular scheduled clinical visits where possible. Placental tissues will be collected after delivery; amniotic fluid will be collected during Caesarean section. Paternal and neonatal blood will also be collected, plus a neonatal stool sample after delivery.