The term ‘multiple pregnancy’ is used to describe the development of more than one fetus in utero at the same time. -Families expecting a multiple birth have different health needs - requiring extra practical support and understanding throughout pregnancy the postnatal period and the early years. - Information and support from well-informed healthcare professionals from the time the multiple pregnancy is diagnosed will help to prepare the parents and avoid potential problems. Multiple pregnancy

The chapter aims to: –describe how types of multiple pregnancy may be distinguished –consider the diagnosis and management of twin pregnancy, the labour and the care of the mother and babies after birth –give an overview of the problems particularly associated with twins and higher order births and the fetal anomalies unique to the twinning process –explain the special needs of the parents and identify the sources of help available.

due to the rise in treatments for infertility such as in vitro fertilization (IVF) and ovulation- stimulating drugs. -The single most important reason for the rise in multiple births is assisted conception although women having children when they are older is a contributory factor -Multiple birth is the greatest single risk to the health and welfare of babies born after IVF due to:

–- the increased rates of stillbirth, preterm birth, neonatal death and disabilities. –2- Maternal complications are also higher with a multiple pregnancy. –3- Concern about the increased morbidity and mortality –4- high costs for health and social care.

Twin pregnancy Types of twin pregnancy -Twins will be either monozygotic (MZ) or dizygotic (DZ). - Monozygotic or uniovular twins are also referred to as ‘identical twins’. - They develop from the fusion of one oocyte and one spermatozoon, which after fertilization splits into two -These twins will be of the same sex and have the same genes, blood groups and physical features, such as eye and hair colour, ear shapes and palm creases. - However, they may be of di ff erent sizes and often have very different personalities and characters.

-Dizygotic or binovular twins develop when two separate oocytes are fertilized by two di ff erent spermatozoa -; they are often referred to as fraternal or non- identical twins. Theyare no more alike than any brother or sister and can be of the same or di ff erent sex. In any multiple pregnancy there is a 50 : 50 chance of a girl or boy, half of dizygotic twins will be boy–girl pairs. -A quarter of dizygotic twins will be both boys and a quarter, both girls. - two-thirds will be dizygotic and one-third monozygotic. -Therefore, approximately one-third of twins are girls, one-third boys and one-third girl– boy pairs.

Determination of zygosity and chorionicity Midwives must understand the di ff erences between these two terms and why it is important. -Determination of zygosity means determining whether or not the twins are monozygotic (identical) or dizygotic (non-identical). -In about one-third of all twins born, it will be obvious as the children will be of a di ff erent sex. -Of the remaining same-sex twins, zygosity will usually be apparent from physical features by the time the children are 2 years old, although parents are not usually prepared to wait this long.

- By the age of 2, parents know their children so well and see their di ff erences in character and personalities that they often find it di ffi cult to believe they are identical. - At birth, monochorionic twins can have a greater weight variation than dichorionic twins. - In approximately two-thirds of monozygotic twins, a monochorionic diamniotic placenta (MCDA) will confirm monozygosity.

-If the babies have a single outer membrane, the chorion, they must be monochorionic and so monozygotic - In one-third of monozygotic twins, the placenta will have two chorions and two amnions (DCDA), and either fused placentas (Fig. 14.2C) or two separate placentas (dichorionic) (Fig. 14.2A), which is indistinguishable from the situation in dizygotic twins.Fig. 14.2CFig. 14.2A

Table 14.2 Relationship between zygosity and chorionicity DichorionicMonochorionicTw o placentae (may be fused)One placentaTw o chorionsOne chorionTw o amnionsTw o amnions (one amnion in monoamniotic tw ins is very rare)These tw ins can be either dizygotic or monozygoticThese tw ins can only be monozygotic

With monozygotic twins the type of placenta produced is determined by the time at which the fertilized oocyte splits: 0–4 days: dichorionic diamniotic placenta DCDA (approx. 33% – 1/3 cases) (Fig A,C)0–4 days: dichorionic diamniotic placenta DCDA (approx. 33% – 1/3 cases) (Fig A,C) 4–8 days: monochorionic diamniotic placenta MCDA (approx. 66% – 2/3 cases) (Fig. 14.2B)4–8 days: monochorionic diamniotic placenta MCDA (approx. 66% – 2/3 cases) (Fig. 14.2B) 8–12 days: monochorionic monoamniotic placenta MCMA (approx. 1% of cases) (Fig. 14.2D)8–12 days: monochorionic monoamniotic placenta MCMA (approx. 1% of cases) (Fig. 14.2D) 12–13 days: (very rare indeed) conjoined twins can develop when the division is incomplete (Bomsel- Helmreich 2005).Bomsel- Helmreich 2005

-Despite the well-established facts about placentation and zygosity, professionals are still giving couples incorrect information. - Same-sex dichorionic twins can be either non- identical or identical and it is only from either an amniocentesis whilst pregnant or deoxyribonucleic acid (DNA) testing after the birth that accurate zygosity can be known.

Chorionicity: why is it important to know? -This knowledge is important clinically because monochorionic twin pregnancies have a 3–5 times higher risk of perinatal mortality and morbidity than dichorionic twin pregnancies (Pasquini et al 2004).Pasquini et al 2004

Zygosity determination after birth The most accurate method of determining zygosity is to compare DNA from each baby. -The DNA can be extracted from cells taken from a cheek swab from inside the mouth. -Specific genetic markers extracted from di ff erent chromosomes are compared and the results are up to 99.99% accurate. -Zygosity determination should be routinely o ff ered to all same-sex dichorionic twins for the following reasons:

Most parents will want to know whether or not their twins are identical, so they can answer the most commonly asked question: ‘Are they identical?’ Also as the twins get older, they usually want to know. If couples are considering further pregnancies, the risk in DZ twin pregnancy increases approximately five-fold: these tend to run in families, usually on the female side. MZ twins do not run in families and the likelihood does not change (except in rare families who carry a dominant gene for monozygotic twinning). The chance of any fertile woman having MZ twins is approximately 1 in 350–400.

It will help the twins in establishing their sense of identity; influence their life and family relationships. The information is important for genetic reasons, not just with monogenic disorders but with any serious illness later in life. Twins are frequently asked to be involved in research and for this knowledge of zygosity is essential.