About a third of the increase in multiple births can be explained by an increasing number of women older than age 30 having children. The remaining two-thirds of the increase can be tied to an increase in the use of fertility medicines and reproductive technology such as in vitro fertilization (IVF). Healthcare providers now closely monitor women who are undergoing fertility treatment so that fewer babies will be produced. Women who have a family history of twins are more likely to have twins of their own. Women who are obese are also at higher risk for having twins. African-American women are also more likely to have twins.

These days, twins and other multiples are rarely a surprise at birth. Most multiple births are discovered with an ultrasound given near the end of the first trimester. Your healthcare provider also may hear more than one fetal heart beating during an exam. Other symptoms of multiple births include more rapid weight gain than expected in the first trimester; a larger uterus than expected; and severe morning sickness.

The average gestation for triplets is 32 weeks, and 30 weeks for quadruplets. More than 90% of triplets are born preterm, and nearly all quadruplets are born preterm.

Premature infants also may have respiratory problems because their lungs have not fully developed. The closer an infant is to its due date, the less likely the child is to have health problems. Some of the health problems may be long term: intellectual disability, and vision and hearing loss.

Identical twins begin as one fertilized egg that divides in half. The other two-thirds of twins are fraternal; they are formed from two separate eggs fertilized by two different sperm. Fraternal twins are no different from other siblings in the family. Identical twins look alike, are always the same sex, and have the same hair and eye color. Fraternal twins often look different, even when they are the same sex; they have a greater variation in size than identical twins, both at birth and as they grow and develop.

Preeclampsia is high blood pressure that develops during pregnancy. Gestational diabetes is a form of diabetes that develops during pregnancy. These health problems can be treated. That's why prenatal care is critical for any woman who is pregnant.

When carrying multiples(twins, triplets, and beyond), pregnant overweight women usually gain 31 to 50 pounds and obese pregnant women usually gain 25 to 42 pounds. Your healthcare provider can make recommendations for you based on your weight and health. A pregnant woman carrying multiples usually needs to consume about 2,700 calories daily.

Discuss with your healthcare provider any special nutritional needs you may have. In general, a woman carrying multiples should take a prenatal vitamin that contains at least 30 mg of iron to prevent anemia and reduce the risk for pre-term delivery. A woman carrying multiples also needs adequate protein, as well as plenty of fluids.

If the infants are likely to be born before 34 weeks, the mother may be given corticosteroids. Corticosteroids encourage earlier development of the babies' lungs. Respiratory problems are common among multiples (and single children) who are born preterm.

A vaginal birth is likely if both babies are positioned with their heads down. Births of 3 or more infants usually require a cesarean delivery, because it is safer. A multiple pregnancy with 3 or more means a crowded uterus, in which the placenta or umbilical cords may be compressed during labor. A cesarean also may be necessary if any of the babies is in a breech position (feet or buttocks down) or transverse lie (sideways).