is not, but most obstetricians will recommend normal delivery unless there are other reasons to avoid vaginal birth. When the first twin is not head down, a caesarean section is often recommended. Regardless of whether the twins are delivered by section or vaginally, the medical literature recommends delivery of dichorionic twins at 38 weeks, and monochorionic twins (identical twins sharing a placenta) by 37 weeks due to the increased risk of stillbirth in monochorionic twins who remain in utero after 37 weeks. The consensus is that late preterm delivery of monochorionic twins is justified because the risk of stillbirth for post-37-week delivery is significantly higher than the risks posed by delivering monochorionic twins near term (i.e., 36–37 weeks). The consensus concerning monoamniotic twins (identical twins sharing an amniotic sac), the highest risk type of twins, is that they should be delivered by caesarean section at or shortly after 32 weeks, since the risks of intrauterine death of one or both twins is higher after this gestation than the risk of complications of prematurity. In a research study widely publicized, singleton children born earlier than 39 weeks may have developmental problems, including slower learning in reading and math. Other risks include: Wet lung (Transient Tachypnea of the Newborn): Failure to pass through the birth canal does not expose the baby to cortisol and epinephrine which typically would reverse the potassium/sodium pumps in the baby's lung. This causes fluid to remain in the lung. Potential for early delivery and complications: Preterm delivery may be inadvertently carried out if the due-date calculation is inaccurate. One study found an increased complication risk if a repeat elective caesarean section is performed even a few days before the recommended 39 weeks. Higher infant mortality risk: In caesarean sections performed with no indicated medical risk (singleton at full term in a head-down position with no other obstetric or medical complications), the risk of death in the first 28 days of life has been cited as 1.77 per 1,000 live births among women who had caesarean sections, compared to 0.62 per 1,000 for women who delivered vaginally. Birth by caesarean section also seems to be associated with worse health outcomes later in life, including overweight or obesity, problems in the immune system, and poor digestive system. However, caesarean deliveries are found to not affect a newborn's risk of developing food allergy. This finding contradicts a previous study that