There has been a dramatic increase in the occurrence of so called high order multiple gestations, those with triplets, quadruplets, quintuplets and beyond. Most of these pregnancies are created in the process of overcoming infertility.
Human reproduction is most efficient when there is only one fetus.
Two factors affect the expected gestational age at delivery. A more important factor is if the mother has had a previous pregnancy and delivery. This experience is worth about two weeks of gestational age at time of delivery. These pregnancies are at risk for early preterm delivery and severe preeclampsia, which puts the babies and mothers at risk for death and long term handicaps in the survivors. Additionally, the economic impact of a premature delivery is potentially catastrophic.