Multiple gestation or multiple pregnancy is a term used to describe a pregnancy with more than one fetus. The vast majority of such pregnancies are cases of twins. The rate of twinning in different populations is determined by racial predisposition to double ovulation. Other terms associated with multiple fetuses are
- Triplets : 3 fetuses
- Quadruplets : 4 fetuses
- Quintuplets : 5 fetuses
- Sextuplets : 6 fetuses
- Septaplets : 7 fetuses
- Octaplets : 8 fetuses
- Nonuplets : 9 fetuses
- Decuplets : 10 fetuses
A multiple birth is the culmination or result of one multiple pregnancy where the woman delivers two or more offspring. When the woman produces more than one egg during ovulation, each of those eggs can get fertilised by a sperm after sexual intercourse to for multiple zygotes. Each single zygote may produce a single embryo or it may split into two or more embryos each carrying the same genetic material. Fetuses that result from different zygotes are called “fraternal” and share only 50% of genetic material. Fetuses from the same zygote share a 100% genetic material and are called “identical” and are always of the same sex.
A multiple pregnancy from single zygote is termed monozygotic and from two zygotes is called dizygotic. Generally, multiple pregnancies of two or more zygotes are termed polyzygotic. The lowest rates are seen in Asia. The zygosity if twins for example, can further be differentiated based on the nature of the two membranes that surrounds the fetuses called chorion and amnion. We can have
- Dichorionic diamnionic dizygomatic twins
- Dichorionic diamnionic monozygomatic twins
- Monochorionic diamnionic twins
- Monochorionic monoamnionic twins
Multiple pregnancies can occur either naturally as a result of multiple ovulation or as a result of infertility treatments such as InVitro Fertilisation (IVF) or fertility drugs. During labour, it is possible to find the fetuses with malpresentations which makes delivery difficult vaginally. Malpresentation may be of one or both fetuses coming with the buttocks, sideways or head. They include
- Vertex – vertex presentation (45%) which is normal.
- Vertex – breech malpresentation (37%).
- Breech – breech malpresentation (10%).
- Vertex – transverse malpresentation (5%).
- Breech – transverse malpresentation (2%).
- Transverse – transverse malpresentation (0.5%).
Risk factors for multiple gestation
Some risk factors have been associated with twinning.Monozygomtic twinning appears to be a chance and is poorly understood.
- West Africans are said to have the highest rates of twinning in the world with an incidence of 1 in 44 pregnancies.
- Dizygomatic twinning is commoner in the female relations of women who are or have had dizygomatic twins.
- Twinning is also common in women of high parity and in those of older ages at the time of conception.
- Dizygomatic twinning is commoner in tall and obese women.
Diagnosis of Multiple gestation
The diagnosis of multiple gestation may be suspected on history and physical examination. A history of infertility treatment or severe hyperemesis or vomiting during early pregnancy are suggestive.
Uterus which is larger than the expected gestational age may indicate multiple pregnancy. Other causes that can result in large-for-date uterus such as polyhydramnios, fibroid, abdominal cysts, hydatidiform mole and retention of urine should be ruled out.
Ultrasound scan in early pregnancy is the definitive diagnosis for multiple gestation and ruling out other possible causes of larger than expected uterus.
Management of multiple gestation
- Before 20 weeks of gestation, antenatal care should be conducted in the usual fashion with particular attention to identifying possible complications.
- Dietary advice as well as iron and folic acid supplementation should be greatly emphasised.
- Any bleeding from the vagina which occurs should be treated adequately so as not to progress into inevitable abortion.
- Regular fetal monitoring when fetal compromise is suspected and assessment of alpha fetoprotein (AFP) to rule out fetal abnormalities like down syndrome.
- After 20 weeks gestation, assessment of fetal growth should be regular in order to identify intrauterine growth retardation.
- Complications like preterm labour or pre-eclampsia should be properly managed and fetuses delivered once stabilised.
Complications of multiple gestation
- Minor complications like heartburns, varicose veins, haemorrhoids and other pressure effects.
- Anaemia especially iron deficiency and megaloblastic.
- Placenta praevia from large placental site.
- Pre-eclampsia and eclampsia.
- Premature labour due to bulk pregnancy and polyhydramnios.
- Intrauterine death or intrauterine growth retardation due to placental insufficiency.
- Postpartum haemorrhage.
- Fetal abnormalities like down syndrome and cerebral palsy.
- Perinatal mortality.
- Preterm delivery with low birth weights.
K. P. Hanretty, “Multiple gestation ” Obstetrics illustrated (6th edition)
Wikipedia : “multiple birth ”