Twin pregnancy — the most common form of multiple gestation — can be exciting news as well as a time to understand the risks that come with carrying twins, triplets or more.

Multiple gestation happens when more than one egg fertilized by sperm implants in the uterus or a single fertilized egg splits to create two or more identical embryos.

When one egg splits, the result is identical twins (or multiples). When multiple fertilized eggs grow in the uterus, the multiples are fraternal. Fraternal multiples are more common than identical.

About 3% of births are twins, while births with triplets or more account for less than 0.1% of births, according to national statistics.

Fertility drugs often cause the ovaries to release more than one egg and can result in twins, triplets or more. If more than one embryo is implanted from in vitro fertilization, multiples can result. If you’re over age 35, it’s more likely you’ll release two or more eggs during a menstrual cycle, which increases the likelihood of multiple gestation.

Rarely, a multiple gestation can cause a false negative pregnancy test. What happens is the hormone levels detected by the test are so high, the test shows a negative result. If you’ve missed a menstrual period and have pregnancy symptoms, see your medical provider.

Signs of Twin Pregnancy

Multiple gestation tends to cause more severe morning sickness or breast tenderness and faster weight gain. You may need maternity clothes shortly after discovering your pregnancy, as multiples tend to show sooner. Multiple gestation is most often discovered by an ultrasound.

You may notice the fetus, or fetuses, moving earlier than you expect or moving in more than one area. Your baby bump, or fundal height (the measurement from the top of your pubic bone to the top of your uterus), may be greater than expected for how long you’ve been pregnant.

Compared to a single gestation, you may be more tired, need to urinate more frequently and have a bigger appetite.

It’s common to gain about 50 pounds during a multiple gestation rather than the 30 pounds typical with a single.

Twin Pregnancy Risks

Multiple gestation pregnancies have their own risks. The specialists at Norton Children’s Maternal-Fetal Medicine, part of Norton Women’s Care, have deep experience helping mothers and their babies through their pregnancy. Our specialists will work with your obstetrician and other members of your health care team. If one or more of your babies will need specialized care after birth, any of the appropriate specialists from across Norton Children’s will be brought into the team.

Preterm delivery — prior to 37 full weeks of gestation — is the most common complication of multiples. Twins arrive preterm more than half the time. Triplets and more are almost always preterm.

Babies born preterm may have a greater risk of difficulty breathing, eating and staying warm. Preterm newborns likely spend time in a neonatal intensive care unit (NICU). Norton Children’s has two NICUs — including a top-rated Level IV NICU and the largest in the state with more than 100 beds at Norton Children’s Hospital in downtown Louisville. Norton Women’s & Children’s Hospital in St. Matthews has a Level III NICU.

A Level IV NICU is equipped and staffed to handle the most complex neonatal conditions. A Level III NICU offers prompt and readily available access to a full range of pediatric medical subspecialties.

Maternal-fetal Medicine Specialists on Your Health Care Team

While under the care of our maternal-fetal medicine (MFM) specialists, you can deliver with your obstetrician, typically at your home hospital.

If your baby or babies need care right after birth, Norton Children’s specialists can be at the delivery and ready to jump into action. Then your baby will spend their first days in the top-rated Norton Children’s NICU.

At Norton Children’s Maternal-Fetal Medicine, part of Norton Women’s Care, we look out for your health as well as your baby’s. The team of MFM specialists is dedicated to taking care of the stresses pregnancy can put on your body.

Through our multidisciplinary team of board-certified, specialty-trained maternal-fetal medicine perinatologists and neonatologists, we work closely with you to create a customized plan for your baby’s arrival.