What is Multiple Pregnancy?
A multiple pregnancy is when a woman is pregnant with two or more babies in the uterus. Twins, triplets, or more may be conceived by the fertilization of a single ovum (egg) or by fertilization of more than one ovum. The incidence of multiple births has increased in recent years, which may be attributed largely to the use of fertility drugs and rapid developments in assisted reproductive technology (ART).
A multiple pregnancy is considered as a high-risk pregnancy with potential risks to the mother and the babies, particularly the incidence of premature birth and its associated complications. Careful monitoring is required throughout pregnancy so as to minimize the chance of complications and bring about safe delivery of the babies.
Process of Multiple Pregnancy
Monozygotic or identical twins result from fertilization of a single ovum by a single sperm, and subsequent division of the fertilized ovum to produce two embryos. It is not influenced by factors such as race, maternal age, or heredity. However, fertility treatments, including fertility drugs such as clomiphene citrate and ART such as in vitro fertilization (IVF), have increased the incidence of multiple pregnancies.
- Are always of the same sex.
- The fetuses may share one placenta, but they usually have their own amniotic sac.
- Usually have the same physical appearance, such as identical hair, eye color, skin, and build.
- Have the same genetic features, such as blood type.
- May be “mirror images” of each other, such as one being left-handed while the other is right-handed.
- One major difference between them is that their fingerprints will not match.
Dizygotic or fraternal twins develop due to fertilization of two ova (eggs) by two different sperms. Fraternal twins are more common than identical twins.
- May be of the same or different sexes.
- Each fetus has a separate placenta and separate amniotic sac.
- Resemblance to each other as brothers or sisters but are not identical.
- May or may not have the same blood type.
Factors influencing dizygotic twinning
- Race – most common in Africans, least common in Asians, and intermediate in whites.
- Family history of twins – inherited from the mother’s side of the family.
- Previous twins – a woman bearing dizygotic twins has more chance of recurrence in a subsequent pregnancy.
- Incidence may increase with higher maternal age, peaking between 35 and 45 years of age.
- More likely in women who conceive shortly after stopping long term use of contraceptive pills.
- Fertility stimulating drugs.
- In-vitro fertilization (IVF).
- Monozygotic triplets result from repeated twinning or super-twinning of a single ovum.
- Trizygotic triplets develop by individual fertilization of three simultaneously expelled ova.
- Triplets may also result when there is twinning of two ova, with elimination of 1 of the 4 resulting embryos.
Signs and Symptoms of Multiple Pregnancy
- The uterus may be too large for the date.
- Hyperemesis gravidarum – excessive vomiting of pregnancy.
- Rapid weight gain during the first trimester.
- Higher human chorionic gonadotropin (hCG) levels.
- Large for date uterine size.
- Polyhydramnios – excessive amniotic fluid
- Excessive weight gain.
- On examination, more than 2 poles may be felt.
- Multiple fetal parts may be felt.
- Two or more fetal heart rates may be heard. This is a reliable sign for diagnosis if the heart rates differ by more than 10 beats/minute. The diagnosis may be confirmed by ultrasound.
Maternal Health Issues, Risks, and Complications
Multiple pregnancy is classified as high-risk pregnancy due to increased incidence of :
- Anemia – greater demand for iron by the fetuses may result in maternal anemia. This may be worsened if the mother was already suffering from anemia before becoming pregnant or as a result of poor diet.
- Urinary tract infection.
- Pre-eclampsia and eclampsia.
- Gestational diabetes.
- Pressure symptoms – the large size of the uterus in multiple pregnancy can put increased pressure on the adjacent structures and the pelvic blood vessels.
- Ovarian cysts and ascites (fluid retention in the abdomen) may result from abnormally high levels of chorionic gonadotropin.
- Increased chance of placenta previa due to the large size of the placenta or placentae (more than one placenta).
- All maternal systems, including cardiovascular, respiratory, renal, musculoskeletal, and gastrointestinal systems are under excessive stress in multiple pregnancy.
- Increased nutritional requirements, both for mother and fetuses.
- Increased risk of hemorrhage before, during, and after delivery.
- Uterine inertia.
- Premature separation of the membranes.
- Greater chance of preterm delivery.
- Increased incidence of cesarean section.
- After delivery, caring for more than one baby can be challenging and exhausting.
- Postpartum depression is more common following multiple births, and more so in case of death of one baby.
- Breastfeeding more than one baby may be difficult.
Because of the risks associated with higher order multiple pregnancy, elective termination, such as reducing triplets to twins, may be done by intracardiac potassium chloride before 20 weeks of pregnancy. It may be done for maternal medical conditions, psychological, or socioeconomic reasons. Selective termination may be done if one fetus is detected as abnormal, but it may be risky for the other twin in case of monochorionic pregnancy.
The incidence of cesarean section is higher in twins than in singleton pregnancy, although normal delivery is possible if both the babies are cephalic (head down position) and in the absence of complications.
In case of triplets, quadruplets, or more, cesarean section is the method of choice.
- Increased perinatal mortality.
- Low birth weight.
- Twin-to-twin transfusion syndrome or local shunting of blood. Intermingling blood supply may result in disparate twin size and one being born plethoric and the other anemic. This is likely to happen in monozygotic twins who share a placenta.
- Cord prolapse.
- Spontaneous abortion (miscarriage).
- Growth restricted babies.
- Severe disability.
- Abnormal presentation and position.
Other Complications and Risks
- Second twin is more likely to be affected by premature separation of the placenta, hypoxia, constriction ring dystocia, prolonged anesthesia, or operative manipulation.
- Vanishing twin – one of the fetuses may spontaneously disappear, although twins had been identified in an earlier ultrasound. The remaining twin usually develops normally.
- Congenital anomalies (birth defects), such as conjoined or Siamese twins – this is a rare complication where the 2 babies are born physically connected to each other. They are most commonly joined at the pelvis, chest or head.
- Fetus acardiacus – this is a rare anomaly. The acardiac twin is a parasitic monozygotic fetus without a heart
- Fetus papyraceous – when one fetus dies in the uterus it may mummify and become compressed by the surviving twin. This is an extremely rare occurrence.
- Collision, impaction, and interlocking of twins.
- Increased chances of fetal death as compared to singleton pregnancy.
Article reviewed by Dr. Greg. Last updated on December 4, 2011