An adult's hand holding a premature baby's feet
These 5 Reasons Are Why So Many Babies Come Earlier Than Expected
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When I learned the due date of my firstborn, I treated it as a kind of magic number: This is it! But life had other plans, and my son arrived one week early. Luckily all was well, but that's unfortunately not always the case for the millions of preemies born every year. So what are the reasons why babies come early, turning those birth date expectations upside down for millions of moms?

A baby's due date is calculated at 40 weeks after the first missed period, but "a mother is considered 'full term' at 37 weeks," explains Dr. Monica McHenry Svets, M.D., an OB-GYN at the Cleveland Clinic, in Ohio. "Prior to this time, we loosely divide preterm labors into categories like early versus late preterm." While the majority of women do deliver between 37 and 42 weeks, about 11 percent of mothers give birth prematurely, according to statistics quoted by Parents.

What accounts for the early arrivals? Tons of reasons: some of them related to the mother's health, some to the baby's, and some are factors that can't be controlled. And in some cases, babies come early for no apparent reason. The important thing, of course, is ensuring the safety of both mother and child. "Childbirth is never risk-free, but delivery at 37 weeks or after is fairly safe overall," Dr. Svets tells Romper. "The earlier the delivery, the riskier it is for the fetus." Among the health concerns for a premature infant are infections, intracranial (brain) bleeding, underdeveloped lungs, blindness, deafness, and developmental delays, according to The Mayo Clinic.

If you're expecting, the odds are that your child will be one of the many who arrive on or close to schedule, but these are some of the more common reasons why your baby might have an earlier birthday than anticipated.


The mom develops health issues during pregnancy.

My own first pregnancy was problem-free until my blood pressure suddenly spiked without warning, and my OB recommended inducing labor for safety's sake. "Medical concerns in the mom's pregnancy can cause the baby to be born within the 37th to 39th week of pregnancy: high blood pressure, diabetes, etc.," says Dr. Svets. Even a seemingly simple condition can become problematic during pregnancy. A recent study published in the Journal of Obstetrics & Gynecology of India showed that pregnant women who had urinary tract infections were more likely to go into preterm labor than women who didn't.


Problems develop within the uterus.


Dr. Svets explains that complications involving the womb itself may make it necessary to deliver a baby preterm. Among them are placenta previa, when the placenta covers all or part of the cervix, and placental abruption, when the placenta separates from the uterus. Having too much or too little amniotic fluid (conditions known as polyhydramnios and oligohydramnios) are both risky for the baby, and early delivery may once again be recommended.


It's due to a multiple birth or birth timing.

Twins and other multiples arrive early in about half of all cases, according to Very Well Family; factors such as preterm labor and preeclampsia are more likely in multiple births. Having a second baby less than 18 months after the first raises your risk for prematurity, according to a study published in Obstetrics and Gynaecology. Dr. Svets notes that it's also common for women who have had more than one child to go into labor between the 37th and 39th week.


Genes may be the culprit.

About 40 percent of spontaneous premature birth is due to genetic factors, according to the March of Dimes. Researchers have identified two potential genes — one carried by the mother and one by the baby — that may raise the risk for premature birth. Once more is known about these "prematurity genes," doctors may be able to develop treatments to help prevent early birth in mothers who carry them.


The mother is older or follows a risky lifestyle.

A number of other risk factors can increase the chance of an early or later preterm birth. A large Canadian study reported by the National Institutes of Health found that mothers over 40 had a higher risk of premature birth than younger moms. Smoking, drinking, and/or substance use during pregnancy can also result in a baby arriving earlier than expected, along with a higher risk of birth defects and health issues for the baby, according to the American College of Obstetricians and Gynecologists.

Having a baby right on your due date is a nice coincidence, but it's more important that you and your child stay healthy, no matter when you give birth. Keeping up with your OB visits, following the doctor's advice, and looking after your own well-being will increase the chances of your baby's arriving on or close to term.

Experts: Monica McHenry Svets, M.D., obstetrician/gynecologist, The Cleveland Clinic

Studies cited:

Verma, I., Avasthi, K, and Berry, V. (2014) Urogenital Infections as a Risk Factor for Preterm Labor: A Hospital-Based Case–Control Study. Journal of Obstetrics and Gynecology of India, 10.1007/s13224-014-0523-6

DeFranco, EA, Ehrlich, S, Muglia, LJ (2014) Influence of interpregnancy interval on birth timing. Obstetrics & Gynaecology,

Fuchs, F., et. al. (2018) Effect of maternal age on the risk of preterm birth: A large cohort study. PLoS One, 10.1371/journal.pone.0191002

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