Multiple Gestation Lecture Notes PDF

Multiple gestation (twin pregnancy) Objective 1 ) Definition of multiple pregnancy in particular twin pregnancy. 2) Types of twin & its classifications. 3) Predisposing factors for twin pregnancy 4) Complications associated with twin pregnancy. 5) Management of twin during pregnancy & labour....

Multiple gestation (twin pregnancy) Objective 1 ) Definition of multiple pregnancy in particular twin pregnancy. 2) Types of twin & its classifications. 3) Predisposing factors for twin pregnancy 4) Complications associated with twin pregnancy. 5) Management of twin during pregnancy & labour. 6) Mode of delivery in twin pregnancy. 7) Mode of delivery in multiples pregnancy.  A 21year old primigravida at 15 weeks of gestation is seen for a routine prenatal visit. At her last visit 4 weeks , her uterus was appropriate for size and dates. Today her uterine fundus is palpable at the umbilicus.  What are deferential diagnosis? What are risk factor ? How we can diagnose the condition ? How we can classified the condition: What are its complications: How we can plan for delivery?  Itspregnancies when there is more than one fetus, it occur in 1-2 %. two-thirds are dizygotic and one-third monozygotic.  Risk factor The incidence of dizygotic twins varies with: Ethnic group (up to 5 times higher in certain parts of Africa and half as high in parts of Asia); Maternal age (2 per cent at 35 years); Parity (2 per cent after four pregnancies); Method of conception (20 per cent with ovulation induction); Family history. The incidence of monozygotic twins is similar in all ethnic groups and no identefiable risk factor. classification The classification of multiple pregnancy is based on No of fetuses : twins; triplet; quadruplets; etc. No of fertilized eggs : Zygosity No of placenta : Chorionicity No. of amniotic cavities : amnionicity  Twins monozygotic Dizygotic Monochorionic Monochorionic Dichorionic Monoamniotic Diamnotic Diamnotic (1%) (20%) ((9%) Dichorionic Diamontic (70%) Postconception days to identical twin cleavage Dichorionic -diamnionic 0-3 days(morula) Monochorionic-diamnionic 4-8 days(blastocyst) Monochorionic-monoamnionic 9-12 days(embryonic disk) Conjoind > 12 days (embryo) Types of multiple gestation Dizygotic or non-identical twins_it results from ovulation and subsequent fertilization of more than one oocytes. In such cases the fetuses are genetically different and each twin have their own amniotic sac (diamniotic) and placenta (dichorionic).. Monozygotic twin - result from the splitting of one embryonic mass in to two or more genetically identical fetuses and there may be sharing of the same placenta (monochorionic), amniotic sac (monoamniotic) or even fetal organs (conjoined or Siamese). when the single embryonic mass splits into two within three days of fertilization, which occurs in one-third of monozygotic twins, each fetus has its own amniotic sac and placenta (diamniotic and dichorionic). When embryonic splitting occurs after the 3rd day following fertilization, there are vascular communications within the two placental circulations (monochorionic). Embryonic splitting after the 9th day following fertilization results in monoamniotic monochorionic twins and splitting after the 12th day results in conjoined twins.  Twin pregnancy may be dizygotic (70%) or monozygotic (30%) Dizygotic twins (non-identical) occur from ovulation and subsequent fertilization of two oocytes. This results in dichorionic diamniotic twins, where each fetus has its own placenta and amniotic cavity. Although they always have two functionally separate placentae (dichorionic), the placentae can become anatomically fused together and appear to the naked eye as a single placental mass. They always have separate amniotic cavities (diamniotic) and the two cavities are separated by a thick three-layer membrane (fused amnion in the middle with chorion on either side. The fetuses can be either same-sex or different-sex pairings.  Monozygotic (identical) pregnancies result from fertilization of a single ovum with subsequent division of the zygote. If the zygote splits shortly after fertilization, the twins will each have a separate placenta and thus will be dichorionic diamniotic. Monochorionic diamniotic (20%) pregnancies occur when division of the zygote occurs between days four and eight post-fertilization. The vast majority of monochorionic twins have two amniotic cavities (diamniotic) but the dividing membrane is thin, as it consists of a single layer of amnion alone. Monochorionic monoamniotic (1%) pregnancy occurs when division occurs between days 8 and 12 postfertilization and finally conjoined twins occur when division of the zygote happens after day 13. Split within 3 days of fertilization two placenta & two amniotic cavit Determination of zygosity and chorionicity Zygosity can only be determined by DNA fingerprinting. Prenatally, such testing would require an invasive procedure to sample amniotic fluid (amniocentesis), placental tissue (chorion villus sampling), or fetal blood (cordocentesis).  The best way to determine chorionicity is by an ultrasound examination in the first trimester of pregnancy, its relies on the assessment of fetal gender, number of placentas, and characteristics of the membrane between the two amniotic sacs. In dichorionic twins the inter-twin membrane is composed of a central layer of chorionic tissue sandwiched between two layers of amnion, whereas in monochorionic twins there is no chorionic layer. In dichorionic twins there is an extension of placental tissue into the base of the inter- twin membrane, referred to as the ‘lambda’ sign, whereas in monochorionic twins this sign is absent  Different-sextwins are dizygotic but in about two-thirds of twin pregnancies the fetuses are of the same sex and these may be either monozygotic or dizygotic. Complication of twin pregnancy ANTEPARTUM Anemia increase 3 fold Preeclampsia 3 fold Gestational diabetes 2 fold Thromboembolism 4 fold INTRAPARTUM Preterm (50)% Malpresntation (50)% Cesarean delivery (50)% POSTPARTUM Haemorrhage increase 5 fold Pregnancy complications according to chorionicity Miscarriage and severe preterm delivery Perinatal mortality in twins Intrauterine growth restriction Fetal abnormalities Chromosomal defects and twining Death of one fetus in a twin pregnancy Complications unique to monochorionic twinning. Others with their management.. (Hyperemesis gravidarum,, hypertensive dis,, gestational DM,, anemia ,,hemorrhage …) Pregnancy complications according to chorionicity Miscarriage and severe preterm delivery The most important complication of any pregnancy is delivery before term and especially before 32 weeks. Almost all babies born before 24 weeks die and usually all born after 32 weeks survive, and delivery between 24 and 32 weeks is associated with a high chance of neonatal death and survivors are usually handicapped. In a singleton pregnancy the chance of delivery between 12 and 23 weeks (miscarriage) is about 1 per cent, and the chance of delivery between 24 and 32 weeks is also about 1 per cent. In dichorionic twins the chance of miscarriage is 2 per cent and of delivery at 24-32 weeks is 5 per cent. In monochorionic twins the chances are 12 per cent and 10 per cent respectively. The average gestation at delivery for twins is 37 weeks and therefore about half of twins delivery preterm.  Perinatal mortality in twins The perinatal mortality rate in twins is around six times higher than in singleton, which is almost entirely due to prematurity-related complications, and its twice as high in monochorionic than dichorionic twin due to an additional complication to prematurity is twin-to- twin transfusion syndrome. Intrauterine growth restriction Insingleton pregnancies the birth weight is below the 5th centile for gestation in about 5 per cent of babies. In dichorionic twins the chances of low birth weight is double for each baby than in singletons and therefore the risk that at least one of the fetuses will suffer poor growth is about 20 per cent. In monochorionic twins the chance of poor fetal growth is almost double that of dichorionic twins..  In dichorionic twin pregnancies where one fetus has intrauterine growth restriction, the condition of both fetuses needs to be considered since the potential benefit of delivery for the small fetus must be weighed against the risk of prematurity- related complication in the normally grown twin. In general delivery should be avoided before 32 weeks even if there is evidence of imminent intrauterine death of the smaller twin. Such a policy may not be applicable in the management of monochorionic twins since death of one fetus may result in death or handicap of its co-twin because of complications arising from the presence of placental vascular anastamoses between the two circulations.  Fetal abnormalities The prevalence of structural abnormalities, such as spina bifida, for each fetus in a dichorionic twin pregnancy is the same as in singleton pregnancies and therefore the chance that in such twin pregnancies at least one of the fetuses would be affected is twice as high as in singleton pregnancies. In monochorionic twin pregnancies the risk for abnormalities for each fetus is four times as high as in singleton pregnancies.  Chromosomal defects and twining In monozygotic twin pregnancies chromosomal abnormalities, such as Down’s syndrome as it affect either one or both fetuses. In dizygotic twins, the maternal age-related risk for chromosomal abnormalities for each twin may also be the same as in singleton pregnancies. Therefore, the chance that at least one fetus is affected by a chromosomal defect is twice as high as in singleton pregnancies of the same maternal age. overall prevalence of chromosomal defects in dizygotic twins is higher than in singletons.  Tests for detection of Trisomy 21 using maternal serum biochemistry are not effective in multiple gestations. The best method of screening in twins is by measurement of fetal nuchal translucency thickness in each fetus by ultrasound at 10-14 weeks. If invasive prenatal diagnosis is required , this may be carried out by amniocentesis or chorion villus sampling, but since it is essential that both fetuses are sampled and that the results correspond to the correct fetus, this should always be carried out in specialist centers. Death of one fetus in a twin pregnancy Intrauterine death of a fetus in a twin pregnancy may be associated with a poor outcome for the co-twin but the type and degree of risk is dependent on chorionicity. Second or third trimester intrauterine death of one fetus may be associated with the onset of labour in dichorionic twins, and acute hypotensive episodes in monochorionic twins leading to death or handicap of the co-twin in about 25 per cent of cases, its due to acute haemodynamic shifts from the live to the dead fetus.  Complications unique to monochorionic twinning In all monochorionic twin pregnancies their is placental vascular anastemoses present which allow communication of the two fetoplacental circulations. In some monochorionic twin pregnancies, imbalance in the net flow of blood across the placental vascular arterio- venous communications from one fetus, the donor to the other, the recipient results in twin-to-twin transfusion syndrome (TTTS)  The donor fetus suffers from both hypovolaemia due to blood loss and hypoxia due to placental insuffeciency, as a result there will be compensatory redistribution in the fetal circulation with preferential perfusion of the brain at the expense of the viscera, this fetus becomes growth restricted and oliguric. The recipient fetus exhibits hypervolaemia, leading to polyuria and polyhydramnios, and high output cardiac failure. Severe disease becomes apparent at 18-24 weeks of pregnancy, with the mother complaining of a sudden increase in abdominal girth associated with extreme discomfort.  Common method of treatment is amniocentesis every1-2 weeks and drainage of large volumes of amniotic fluid; this treatment improves survival by prolonging the pregnancy. More recent method involves the introduction of a thin endoscope into the uterus and the use of laser to coagulate the placental blood vessels that connect the circulations of the two fetuses; in about 70 per cent of pregnancies one or both babies survive. Clinical features The clinical features of multiple gestations are related to firstly, the increased uterine size for a given gestation, and secondly, the increased production of pregnancy-related hormones, which leads to exaggeration of the normal maternal responses in pregnancy. In a twin pregnancy, compared to a singleton, the maternal cardiac output, glomerular filtration rate, gastrointestinal changes and haematological changes, due to increase in plasma volume. Pregnancy complications and their management Hyperemesis gravidarum Increased placental hormone production, especially human chorionic gonadotrophin, may lead to severe vomiting in the first trimester. All cases of hyperemesis should therefore undergo an ultrasound scan to diagnose multiple gestation (and other causes such as hydatidiform mole). This complication is managed the same way as in singletons.  Hypertensive disease Pregnancy-associated hypertension occurs about three to five times more commonly in multiple gestations than singletons, and may occur at an earlier gestation and be more severe. Management principles are the same as in singletons.  Gestational diabetes The increase levels of diabetogenic placental hormones in multiple gestation result in a greater prevalence of gestational diabetes and routine screening should be carried out according to local policy.  Anaemia Increased plasma volume expansion and increased feto-placental demand for iron and folic acid lead to an increased prevalence of anaemia which may require dietary supplementation  ‘Minor’ symptoms of pregnancy Gastro-oesophageal reflux, abdominal discomfort, back pain, leg swelling, bladder symptoms and haemorrhoids are all more common and/or severe in multiple gestation due to the increased size of the uterus and the increased placental hormone levels. management is symptomatic, as for singletons.  Antepartum haemorrhage (placenta praevia, placental abruption) Antepartum haemorrhage is a major contributor to perinatal mortality and the prevalence of antepartum haemorrhage is increased in multiple gestations both due to the larger placental area and increase in other complications, such as hypertensive disease, which may lead to placental abruption.  Thromboembolic disease The more marked prothromboembolic physiological alterations and the increased effect of uterine pelvic venous compression leads to increased risk of thromboembolic disease and appropriate prophylaxis and treatment should be given.  Mode of delivery If the first twin is presenting by the vertex and there are no other complications, many obstetricians will allow a vaginal delivery with the same contraindications as for singletons. However, since in some twin vaginal deliveries there may be complications in delivery of the second twin which require an instrumental or operative intervention, some obstetricians prefer to deliver most multiple gestations by elective Caesarean Section. Ultimately, the decision in each case must be based on the previous obstetric history, the presentation, presence or absence of other complications, and maternal preferences. In the presence of previous lower segment Caesarean Section the contraindications for trial of vaginal delivery are the same as in singletons  Postpartum haemorrhage Due to the large placental site and excessive uterine distention with consequent lack of uterine muscle tone, the risk of postpartum haemorrhage is increased in twin pregnancies. Management is as for singletons, but all multiple gestations should have an IV line sited and blood grouped and saved during labour, and an oxytocin infusion is often commenced following delivery.