Chapter 27

### I. Intensive and convalescent care

1. Definitions

1. Multiple gestation births occur when more than one fetus develops during pregnancy.

2. Zygosity determines if multiple gestation births arise from a single fertilized egg (monozygotic) splitting into two or more embryos or from multiple eggs (dizygotic or polyzygotic) that are fertilized and develop separately.

3. Since monozygotic twins carry the same genetic material, they are often referred to as identical. Polyzygotic multiples are genetically similar to siblings from separate pregnancies and are often called fraternal.

4. Classification of the placenta may be useful in determining zygosity. Twin placentation is classified by the placental disk (single, fused, separate), chorion number (monochorionic, dichorionic), and number of amnions (monoamniotic, diamniotic).

5. Different gender twins are always dizygotic and have a dichorionic placenta. Monochorionic twins are monozygotic and always of the same sex.

2. Incidence

1. The incidence of multiple births has steadily increased in developing countries since the early 1980s.

2. Most of the international and temporal variation in twinning is explained by variation in dizygotic twinning. The prevalence of monozygotic (MZ) twin births has been constant worldwide at 3.5/1000 maternities until recently.

3. US data from 2010 show an incidence of 33.1 per 1000 total births. The twinning rate rose more than 70% from 1980 to 2009, but the pace of increase has slowed in recent years.

4. The rate of triplet and higher-order multiple births (triplet/+) in 2010 was 137.6 per 100,000 births. The triplet/+ birth rate rose more than 400% during the 1980s and 1990s, but has declined since 1998.

5. Estimates of the incidence of twin conceptions are difficult mainly by the unknown number of abortions and early fetal deaths that occur in multiple pregnancies.

6. Assisted reproductive technologies (ART) have become widely used in the treatment of infertility over the last 30 years. Currently 1.8% of all births in the UK and 1% of US births occur after assisted conception and in some countries such as Denmark the figure is 4.4%. The most well-documented risk of ART is multiple births with 18% of all multiple births resulting from ART. The majority are dizygotic twins, resulting from multiple embryo transfer.

7. Two-thirds of twins result from dizygosity, while one-third is monozygotic.

3. Pathophysiology

Per above

4. Risk factors

1. Use of ART

2. Previous or family history of twin pregnancy

4. Multiparity

5. Ethnic background (African American>Caucasian>Asian)

5. Clinical presentation and diagnosis

Multiple gestation pregnancies are usually diagnosed by early ultrasound and may result in several complications of pregnancy and delivery.

1. Perinatal mortality

1. The risk of infant death increases with the increasing number of infants in the pregnancy. The perinatal mortality rate is over four times higher in twins and four to nine times higher in triplets.

2. The increased rate of loss in multiples is explained by an increased risk of both stillbirth and neonatal death. The increased risk of stillbirth is unexplained but is strongly associated with chorionicity, and the neonatal deaths to prematurity. Stillbirth and neonatal mortality rates were significantly higher in monochorionic than dichorionic twins. The ...

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