When a woman carries more than one infant in her uterus during pregnancy, they are called "multiples." When a mom gives birth to twins, triplets, quadruplets, quintuplets, sextuplets, or even more babies, it is termed a multiple birth. The babies may be genetically identical or genetically different (fraternal). It is becoming more common for women to carry and give birth to many infants at one time due to assisted reproductive technology (ART). Multiple pregnancy also occurs naturally without the help of medical intervention.
An embryo consists of one single egg fertilized by one sperm. Sometimes, the egg splits in two, resulting in genetically identical twins. If one of these eggs splits again, triplets result. Four or more identical babies may result from eggs that split, but this is much more rare than twins or triplets. However many times an egg splits, the babies will be 100% genetically identical and will be the same gender. Approximately 3 or 4 of every 1,000 live births are identical.
If a woman releases more than one egg per month, it is possible for multiple eggs to become fertilized at the same time. Each egg has distinct genes and is fertilized by different sperm. This results in multiples that are genetically unique, or fraternal. The babies may be different genders. They may appear as alike or dissimilar as any other genetically unique brothers and sisters. Fraternal multiples are more common than identical ones.
A woman is fertile for a certain amount of days every month. If a woman releases two or more eggs during this fertile period, the eggs may be fertilized at different times. If a woman has more than one sexual partner around the time of ovulation, it is even possible for the eggs to be fertilized by different men. Multiples may be conceived at different times by different fathers in the same pregnancy.
Many parents of twins notice the children have unique ways of communicating with each other. They may even have their own secret language. One study of twins in utero found that by the 14th week of gestation, the infants make specific movements towards each other. The movements are intentional and not accidental. Additional studies are needed to see if the same behavior occurs with triplets, quadruplets, and other multiples.
Women who are pregnant with two or more babies may give birth via a cesarean section, or C-section. The doctor makes an incision in the lower abdomen and uterine wall to deliver the babies. Women who carry two or more infants at a time may experience more potential complications by trying to give birth vaginally. In cases in which the health of the mother or the infants is at risk, C-section birth may be necessary. Many twins and most triplets and greater numbers of multiples are born via C-section.
Fertility treatment increases the chance that a woman may conceive more than one baby at a time. Some fertility drugs increase the number of eggs released by the ovaries. More eggs mean a female has more chances to get pregnant. It also means she is more likely to get pregnant with fraternal multiples.
This is a type of assisted reproductive technology (ART) in which a female is first given fertility drugs. Eggs are then harvested and fertilized with sperm in a laboratory procedure. The resulting embryos are then implanted within the female's uterus. Sometimes, two or more embryos are placed within the uterus to increase the chance of a successful pregnancy. With this procedure, a female may end up carrying more than one embryo if more than one implant successfully.
African-American females have twins more often than women of other races. Asian females are least likely to have twins. A little more than one-third of American females over the age of 30 have babies. Women over the age of 30 are more likely to release two or more eggs during ovulation, so older females are more likely to become pregnant with more than one baby. This is a natural phenomenon that occurs without infertility treatment. Hormonal factors are likely responsible for the effect.
Mothers who carry more than one baby at a time are an average of 1 inch taller than moms who carry single babies. Tall women tend to have higher levels of insulin-like growth factor (IGF), a hormone that may be responsible for the effect. This hormone stimulates the ovaries to release many eggs at once.
One study found that women who consumed milk and dairy products were more likely to have a multiple pregnancy than women who were vegan. Vegan females had twins at one-fifth the rate that vegetarian and omnivorous females did. The effect was especially pronounced in regions where the cattle were treated with growth hormones. Consuming dairy products from cows treated with growth hormone is supposed in the study to increase insulin-like growth factor, a hormone that stimulates the ovaries to release more eggs. However a different study concludes there is no difference in the level of hormones found in milk from treated cows compared to conventional milk.
Multiple pregnancy runs in families. A woman who has a sister or mother who has fraternal twins is approximately twice as likely to have fraternal twins herself. Females who have a higher body mass index (BMI) are also more likely to have fraternal twin pregnancies. BMI is an indicator of body fat. Having a BMI that is higher than ideal is bad for your overall health.
When a mom is pregnant with more than one baby, preterm delivery is very common. Newborns who are delivered under 37 weeks are considered preterm and likely to have low birth weight. Early delivery is a common risk of multiple pregnancy. Infants delivered at 39 or 40 weeks of gestation are considered full-term. Newborns born before 32 weeks of are more likely to suffer from long-term health problems including vision issues, hearing loss, cerebral palsy, and potentially brain damage. During pregnancy, doctors watch for signs of fetal distress and monitor for the possibility of preterm birth.
Preeclampsia is a condition in which pregnant mothers develop high blood pressure and possibly vision problems, headaches, vomiting, and nausea. Any pregnant mom can develop the condition but it is more common in multiple pregnancy. The condition is treatable with medication. Preeclampsia typically goes away after delivery. Frequent and adequate prenatal care decreases the risk that mom and babies will develop complications due to preeclampsia.
Moms with multiple pregnancy have a higher risk of potential complications, so frequent check-ups are necessary. Fetuses are also at increased risk in multiple pregnancy. The doctor will track fetal growth and development. The physician will monitor mom's weight, blood pressure, blood sugar, and other factors. The doctor will also look for signs of early labor.
IMAGES PROVIDED BY:
- American Pregnancy Association: “Complications in a Multiples Pregnancy," “How a Multiples Pregnancy Occurs.”
- Centers for Disease Control and Prevention: “Assisted Reproductive Technology.”
- Journal of the American Dietetic Association: “Survey of retail milk composition as affected by label claims regarding farm-management practices.”
- The Journal of Reproductive Medicine: “Mechanisms of Twinning: VII. Effect of Diet and Heredity on the Human Twinning Rate.”
- National Vital Statistics Reports: “Births: Final Data for 2013.”
- Obstetrics and Gynecology: “Relationship of Maternal Body Mass Index and Height to Twinning.”
- PLoS One: “Wired to Be Social: The Ontogeny of Human Interaction.”