Why does fsh increase the incidence of multiple births

DZ twins occur when two eggs are released at the same time and are fertilized by two different sperm. The older a woman is, the higher her chance of having DZ twins.

This may be due to the higher level of follicle-stimulating hormone FSH that older women have as they approach menopause. FSH stimulates ovulation, and an increased level may cause multiple eggs to be released. So while older women are statistically less likely to get pregnant, if they do get pregnant, they are more likely to have DZ twins.

Non-identical twins occur when two separate eggs are each fertilized by a separate sperm. The two embryos that result are dizygotic, not genetically identical, and can be the same or different sex. Most of the time, this is the type of twinning that occurs from assisted reproduction procedures. Spontaneous losses are even higher in triplet and quadruplet pregnancies.

When a fetus is lost in the first trimester, the remaining fetus or fetuses generally continue to develop normally, although vaginal bleeding may occur. Ultrasound examinations performed early in the 5th week of pregnancy occasionally may fail to identify all fetuses. After 6 to 8 weeks, ultrasound should provide an accurate assessment of the number of fetuses.

Naturally, twins occur in about one in pregnancies, triplets in about one in 10, pregnancies, and quadruplets in about one in , pregnancies. The main factor that increases your chances of having a multiple pregnancy is the use of infertility treatment, but there are other factors. Your race, age, heredity, or history of prior pregnancy does not increase your chance of having identical twins but does increase your chance of having fraternal twins. Infertility treatment increases your risk of having twins, both identical and fraternal.

The overall rate of twins for all races in the United Statees is around 33 per 1, live births. Black and non-Hispanic white women have similar rates of twinning, while Hispanic women are less likely. Non-identical twin women give birth to twins at the rate of 1 set per 60 births. However, non-identical male twins father twins at a rate of 1 set per births.

Maternal age and prior pregnancy history. The frequency of twins increases with maternal age and number of pregnancies. Women between 35 to 40 years of age with 4 or more children are 3 times more likely to have twins than a woman under 20 without children. Maternal height and weight. Non-identical twins are more common in large and tall women than in small women.

This may be related more to nutrition than to body size alone. During World War II, the incidence of non-identical twinning decreased in Europe when food was not readily available. Fertility Drugs and Assisted Reproductive Technology. Multiple pregnancy is more common in women who utilize fertility medications to undergo ovulation induction or superovulation. Use of drugs to cause superovulation has caused the vast majority of the increase in the multiples.

Assisted reproductive technology ART procedures such as in vitro fertilization IVF also contribute to the increase in the multiple birth rate. The risk of multiple pregnancy increases as the number of embryos transferred increases. The duration of a normal singleton pregnancy ranges from 37 weeks to 42 weeks from the time of the last menstrual period.

Twin pregnancies occasionally progress to 40 weeks but almost always deliver early. As the number of fetuses increases, the expected duration of the pregnancy decreases. The average duration is 35 weeks for twins, 33 weeks for triplets, and 30 weeks for quadruplets.

Complications increase with each additional fetus in a multiple pregnancy and include many medical issues that will be discussed below. In addition to these, there is a higher incidence of severe nausea and vomiting, cesarean section, or forceps delivery. If you are pregnant with twins or more, or if you are at risk for a multiple pregnancy, you should be aware of these and other potential problems you might experience. Preterm labor and birth pose the greatest risk to a multiple pregnancy.

Cesarean section is often needed for twin pregnancies and is expected for delivery of triplets. Since preterm labor and birth present such serious risks, the pregnant mother must understand the warning signs of early labor. Sometimes, preterm delivery can be delayed by a few days or more if it is detected early.

Each day gained provides valuable fetal growth and development. Once a woman is in advanced labor, delivery cannot be stopped. In rare instances, delivery of a second twin can be delayed. This delay, when possible, allows for continued growth in the protective environment of the uterus. Currently, there are no effective treatments to prevent preterm birth of multiples. The placenta is attached to the wall of the uterus, and the fetus is attached to the placenta by the umbilical cord.

The placenta provides blood, oxygen, and nutrition to the fetus through the umbilical cord. Placental function is more likely to be abnormal in a multiple pregnancy. If the placenta is unable to provide adequate oxygen or nutrients to the fetus, the fetus cannot grow properly. The placenta ages prematurely and may slow fetal growth, especially late in the third trimester.

Another placental problem is twin-twin transfusion, a life-threatening condition in identical twins. This transfusion occurs when blood flows from one fetus to the other through a connection in a shared placenta.

Therapeutic amniocentesis and laser coagulation of blood vessels that link circulation to the twins in the placenta s may reduce complications of twin-twin transfusion. Preeclampsia, also known as toxemia, occurs 2 to 5 times more often in multiple pregnancies.

The condition may progress and threaten the health of the mother and baby. When severe, the mother may have seizures, and stroke or other life-threatening complications are possible. Women with multiple pregnancies are more likely to develop gestational diabetes during pregnancy. Babies of diabetic mothers are more likely to experience respiratory distress and other newborn complications. Oxford University Press is a department of the University of Oxford.

It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account.

Sign In. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume Article Contents Abstract. Subjects and methods. The paradox of declining fertility but increasing twinning rates with advancing maternal age.

Beemsterboer , S. E-mail: r. Oxford Academic. Google Scholar. Revision received:. Cite Cite S. Select Format Select format. Permissions Icon Permissions. Figure 1. Open in new tab Download slide. All rights reserved. For Permissions, please email: journals. Issue Section:. Principles of Medical Therapy in Pregnancy. Steinman G. Mechanisms of twinning: VIII.

Maternal height, insulin-like growth factor and twinning rate. J Reprod Med. Mechanisms of twinning. Sex preference and lactation. Shur N. The genetics of twinning: from splitting eggs to breaking paradigms. University of Rochester Medical Center. Health Encyclopedia.

Overview of Multiple Pregnancy. Centers for Disease Control and Prevention. Blastocyst culture is associated with an elevated incidence of monozygotic twinning after single embryo transfer. Fertil Steril. Case report: Successful of a spontaneous quadruplet pregnancy. J Prenat Med. Fertility treatments and multiple births in the United States. N Engl J Med. Multiples: Twins, Triplets and Beyond. March of Dimes. Mechanisms of twinning: X. The male factor. Your Privacy Rights. To change or withdraw your consent choices for VerywellFamily.

At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data. We and our partners process data to: Actively scan device characteristics for identification.

I Accept Show Purposes. Table of Contents View All. Table of Contents. Causes of Twins. Odds of Having Twins. How Common Are Twins? Odds of Identical Twins.