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Multiple pregnancy

Extracted from Survival Guide to Midwifery, 2nd Edition (2012) Diane M. Fraser and Margaret A. Cooper, Oxford; Churchill Livingstone: 2012. Courtesy Elsevier

The term multiple pregnancy describes the development of more than one fetus in the uterus at the same time.

Twin pregnancy

Types of twin pregnancy

Twins will be either monozygotic (MZ) or dizygotic (DZ). In the UK, approximately two-thirds will be DZ and one-third MZ. Superfecundation is the term used when twins are conceived from sperm from different men if a woman has had more than one partner during a menstrual cycle. It is not known how often this happens, but if suspected then paternity can be checked by DNA testing. Superfetation is the term used for twins conceived as the result of two coital acts in different menstrual cycles. This is thought to be very rare.

 

Monozygosity and dizygosity

Monozygotic or uniovular twins

  • Also referred to as 'identical twins'
  • Develop from the fusion of one oocyte and one spermatozoon, which after fertilisation splits into two
  • Are 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; may be of different sizes and sometimes have different personalities

Dizygotic or binovular twins

  • Also referred to as 'non-identical twins'
  • Develop from two separate oocytes that are fertilised by two different spermatozoa
  • Are no more alike than any brother or sister and can be of the same or different sex

Diagnosis of twin pregnancy

This is usually through ultrasound examination. Diagnosis can be made as early as 6 weeks into the pregnancy, or later at the routine detailed structural scan between the 18th and 20th weeks. A family history of twins should alert the midwife to the possibility of a multiple pregnancy. Occasionally (1 in 12 000 live births), one fetus may die in the second trimester and become a fetus papyraceous, which becomes embedded in the surface of the placenta and expelled with the placenta at delivery.

Abdominal examination

Inspection

  • The size of the uterus may be larger than expected for the period of gestation, particularly after the 20th week. The uterus may look broad or round
  • Fetal movements may be seen over a wide area, although the findings are not diagnostic of twins
  • Fresh striae gravidarum may be apparent
  • Up to twice the amount of amniotic fluid is normal in a twin pregnancy but polyhydramnios is not an uncommon complication of a twin pregnancy, particularly with monochorionic twins

Palpation

  • The fundal height may be greater than expected for the period of gestation
  • The presence of two fetal poles (head or breech) in the fundus of the uterus may be noted; multiple fetal limbs may also be palpable
  • The head may be small in relation to the size of the uterus
  • Lateral palpation may reveal two fetal backs or limbs on both sides
  • Pelvic palpation may give findings similar to those on fundal palpation, although one fetus may lie behind the other and make detection difficult
  • Location of three poles in total is diagnostic of at least two fetuses

Auscultation

  • Hearing two fetal hearts is not diagnostic; however, if simultaneous comparison of the heart rates reveals a difference of at least 10 beats per minute, it may be assumed that two hearts are being heard

     

The pregnancy

A multiple pregnancy tends to be shorter than a single pregnancy. The average gestation for twins is 37 weeks, for triplets 34 weeks, and for quadruplets 33 weeks.

Effects of pregnancy

Exacerbation of common disorders

More than one fetus and the higher levels of circulating hormones often exacerbate the common disorders of pregnancy. Sickness, nausea and heartburn may be more persistent and more troublesome than in a singleton pregnancy.

Anaemia

Iron deficiency and folic acid deficiency anaemias are common. Early growth and development of the uterus and its contents make greater demands on the maternal iron stores; in later pregnancy (after the 28th week) fetal demands may lead to anaemia. Routine prescription of iron and folic acid supplements is not necessary.

Polyhydramnios

This is particularly associated with monochorionic twins and with fetal abnormalities. Polyhydramnios will add to any discomfort that the woman is already experiencing. Acute polyhydramnios can lead to miscarriage or premature labour.

Pressure symptoms

Impaired venous return from the lower limbs increases the tendency to varicose veins and oedema of the legs. Backache is common and the increased uterine size may also lead to marked dyspnoea and to indigestion.

Other effects

There can be an increase in complications of pregnancy.

Antenatal screening

  • Nuchal translucency for Down syndrome is accurate only if performed between 11 and 13 weeks.
  • Serum screening is not usually performed in multiple pregnancy, as results are too complex to interpret.
  • Chorionic villus sampling (CVS) is not usually recommended in multiple pregnancy, as loss rates are high.
  • Amniocentesis can be performed in twin pregnancies, usually between 15 and 20 weeks. It should be performed in a specialist fetal medicine unit. Most obstetricians prefer to do a dual needle insertion so there is no chance of contamination between the two sacs.
  • Chorionicity should be determined in the first trimester.
  • All MZ twins should have echocardiography performed at approximately 20 weeks' gestation, as there is a much higher risk of cardiac anomalies in these babies.

Ultrasound examination

  • Monochorionic twin pregnancies should be scanned every 2 weeks from diagnosis to check for discordant fetal growth and signs of twin-to-twin transfusion syndrome (TTTS).
  • Dichorionic twin pregnancies should be scanned at 20 weeks for anomalies, and then usually every 4 weeks.

Antenatal preparation

Early diagnosis of a twin pregnancy and of chorionicity is extremely important in order to support and advise the parents.

Preparation for breastfeeding

Mothers should be advised not only that it is possible to breastfeed two, and in some cases three, babies, but also that, nutritionally, this is the best way for her to feed her babies.

Labour and birth

Onset of labour

The higher the number of fetuses the mother is carrying, the earlier the labour is likely to start. Term for twins is usually considered to be 37 weeks rather than 40, and approximately 30 per cent of twins are born preterm. In addition to being preterm the babies may be small for gestational age and therefore prone to the associated complications of both conditions. If spontaneous labour begins very early the mother may be given drugs to inhibit uterine activity. Known causes of preterm labour, for example urinary tract infection, should be treated with antibiotics. It is very unusual for a twin pregnancy to last more than 40 weeks; many obstetricians advise induction of labour at 38 weeks. If the first twin is in a cephalic presentation, labour is usually allowed to continue normally to a vaginal birth, but if the first twin is presenting in any other way, an elective caesarean section is usually recommended.

Management of labour

Induction of labour usually occurs around 38 weeks' gestation. The presence of complications such as pregnancy-induced hypertension, intrauterine growth restriction or twin-to-twin transfusion syndrome may be reasons for earlier induction. The majority will go into labour spontaneously. There is an increased incidence of dysfunctional labour in twin pregnancies, possibly because of overdistension of the uterus.

  • Continuous fetal heart monitoring of both babies is advocated. This can be achieved with two external transducers, or once the membranes are ruptured, with a scalp electrode on the presenting twin and an external transducer on the second.
  • If a 'twin monitor' is available, both heartbeats can be monitored simultaneously to give a more reliable reading. Uterine activity will also need to be monitored.
  • If cardiotocography (CTG) is not available, use of Doppler fetal monitoring may give more accurate recordings of the fetal heart rates than a fetal stethoscope. If the latter has to be used, two people must auscultate simultaneously so that fetal heart rates are counted over the same minute.

Mobilisation or the adoption of whichever position the mother finds most comfortable should be encouraged. A foam rubber wedge under the side of the mattress will help to prevent supine hypotensive syndrome by giving a lateral tilt. A birthing chair or a reclining chair may be more comfortable than a delivery bed. Regional epidural block provides excellent analgesia and, if necessary, allows easier instrumental deliveries and also manipulation of the second twin. The use of inhalation analgesia may be helpful, either before the epidural is in situ or during the second stage if the effect of the epidural is wearing off.

  • If fetal compromise occurs during labour, delivery will need to be expedited, usually by caesarean section. Action may also need to be taken if the mother's condition gives cause for concern.
  • If uterine activity is poor, the use of intravenous oxytocin may be required once the membranes have been ruptured.
  • If the babies are expected to be premature and of low birth weight or known to have any other problems, the neonatal unit must be informed.

Management of the births

The second stage of labour may be confirmed by a vaginal examination. The obstetrician, paediatric team and anaesthetist should be present for the births because of the risk of complications.

  • If epidural analgesia has been used, it may be 'topped up'.
  • The possibility of emergency caesarean section is ever-present and the operating theatre should be ready to receive the mother at short notice.
  • Monitoring of both fetal hearts should continue.
  • Provided that the first twin is presenting by the vertex, the birth can be expected to proceed normally.
  • When the first twin is born, the time of birth and the sex are noted, and the baby and cord must be labelled as 'twin one' immediately.
  • The baby may be put to the breast because suckling stimulates uterine contractions.
  • If the first baby requires active resuscitation, the paediatric team will take over.
  • After the birth of the first twin, abdominal palpation is carried out to ascertain the lie, presentation and position of the second twin and to auscultate the fetal heart:
  • If the lie is not longitudinal, an attempt may be made to correct it by external cephalic version.
  • If it is longitudinal, a vaginal examination is made to confirm the presentation.
  • If the presenting part is not engaged, it should be guided into the pelvis by fundal pressure before the second sac of membranes is ruptured.
  • The fetal heart should be auscultated again once the membranes are ruptured.
  • If uterine activity does not recommence, intravenous oxytocin may be used to stimulate it.
  • When the presenting part becomes visible, the mother should be encouraged to push with contractions to birth the second twin.
  • The reduced size of the placental site following the birth of the first twin means that the second fetus may be somewhat deprived of oxygen.
  • The birth of the second twin should be completed within 45 minutes of the first twin as long as there are no signs of fetal distress in the second twin; if there are, the birth must be expedited and the second twin may need to be delivered by caesarean section.
  • A uterotonic drug is usually given intramuscularly or intravenously, depending on local policy, after the birth of the anterior shoulder.
  • Record the time of birth and sex of this baby, and label the baby and cord as 'twin two'
  • The risk of asphyxia is greater for the second twin. The baby may need to be transferred to the neonatal unit but shown to the mother prior to transfer.
  • Once the uterotonic drug has taken effect, controlled cord traction is applied to both cords simultaneously and the placentae should be delivered without delay. Emptying the uterus enables bleeding to be controlled and postpartum haemorrhage (PPH) prevented. An infusion of 40 IU of Syntocinon in 500 ml of normal saline should be prepared for prophylactic use in the management of PPH.
  • The placenta(e) should be examined and the number of amniotic sacs, chorions and placentae noted. Pathological examination of placentae and membranes may be needed to confirm chorionicity.

Complications associated with multiple pregnancy

The high perinatal mortality associated with twinning is largely due to complications of pregnancy, such as the premature onset of labour, intrauterine growth restriction and complications of delivery.

Polyhydramnios

Acute polyhydramnios may occur as early as 18-20 weeks. It may be associated with fetal abnormality but it is more likely to be due to TTTS.

Twin-to-twin transfusion syndrome

Also known as fetofetal transfusion syndrome (FFTS), this can be acute or chronic. The acute form usually occurs during labour and is the result of a blood transfusion from one fetus (donor) to the other (recipient) through vascular anastomosis in a monochorionic placenta. Both fetuses may die of cardiac failure if not treated immediately. Chronic FFTS can occur in up to 35% of monochorionic twin pregnancies and accounts for 15-17% of perinatal mortality in twins. The placenta transfuses blood from one twin fetus to the other. Fetal and/or neonatal mortality is high but some infants may be saved by early diagnosis and prenatal treatment. Selective fetocide is sometimes considered.

Fetal abnormality

This is particularly associated with MZ twins.

Conjoined twins

This extremely rare malformation of MZ twinning results from the incomplete division of the fertilised oocyte. Delivery has to be by caesarean section. Separation of the babies is sometimes possible and will depend on how they are joined and which internal organs are involved.

Acardiac twins (twin reversed arterial perfusion - TRAP)

One twin presents without a well-defined cardiac structure and is kept alive through placental anastomoses to the circulatory system of the viable fetus.

Fetus-in-fetu (endoparasite)

Parts of one fetus may be lodged within another fetus; this can happen only in MZ twins.

Malpresentations

The fetuses can restrict each other's movements, which may result in malpresentations, particularly of the second twin. After the birth of the first twin, the presentation of the second twin may change.

Premature rupture of the membranes

Malpresentations due to polyhydramnios may predispose to preterm rupture of the membranes.

Prolapse of the cord

This is associated with malpresentations and polyhydramnios and is more likely if there is a poorly fitting presenting part. The second twin is particularly at risk.

Prolonged labour

Malpresentations are a poor stimulus to good uterine action and a distended uterus is likely to lead to poor uterine activity and consequently prolonged labour.

Monoamniotic twins

Monoamniotic twins risk cord entanglement with occlusion of the blood supply to one or both fetuses. Delivery is usually at around 32-34 weeks and by caesarean section.

Locked twins

This is a rare but serious complication. There are two types: one occurs when the first twin presents by the breech and the second by the vertex, the other when both are vertex presentations. In both instances the head of the second twin prevents the continued descent of the first.

Delay in the birth of the second twin

After delivery of the first twin, uterine activity should recommence within 5 minutes. Birth of the second twin is usually completed within 45 minutes of the first birth. In the past the birth interval was limited to 30 minutes in an attempt to minimise complications. With the introduction of fetal heart rate monitoring the interval time between babies is not so crucial as long as the fetal condition is monitored. Poor uterine action as a result of malpresentation may be the cause of delay. The risks of delay are:

  • Intrauterine hypoxia
  • Birth asphyxia following premature separation of the placenta
  • Sepsis as a result of ascending infection from the first umbilical cord, which lies outside the vulva.

After the birth of the first twin the lower uterine segment begins to reform and the cervical canal may have to dilate fully again. The midwife may need to 'rub up' a contraction and to put the first twin to the mother's breast to stimulate uterine activity.

  • If there appears to be an obstruction, a caesarean section may be necessary.
  • If there is no obstruction, oxytocin infusion may be commenced or forceps delivery considered.

Premature expulsion of the placenta

The placenta may be expelled before delivery of the second twin.

  • In dichorionic twins with separate placentae, one placenta may be delivered separately.
  • In monochorionic twins, the shared placenta may be expelled. The risks of severe asphyxia and death of the second twin are then very high.
  • Haemorrhage is also likely if one twin is retained in utero, as this prevents adequate retraction of the placental site.

Postpartum haemorrhage

Poor uterine tone as a result of overdistension or hypotonic activity is likely to lead to postpartum haemorrhage.

Undiagnosed twins

The possibility of an unexpected undiagnosed second baby should be considered if the uterus appears larger than expected after the birth of the first baby or if the baby is surprisingly smaller than expected. If an uterotonic drug has been given after the birth of the anterior shoulder of the first baby, the second baby is in great danger and delivery should be expedited. He or she will require active resuscitation because of severe asphyxia.

Postnatal period

Care of the babies

Immediate care at delivery is the same as for a single baby. Identification of the infants should be clear and the parents should be given the opportunity to check the identity bracelets and cuddle their babies.

Nutrition

Both babies may be breastfed, either simultaneously or separately. The mother may choose to feed artificially.

  • If the babies are small for gestational age or preterm, the paediatrician may recommend that the babies be 'topped up' after a breastfeed. Expressed breast milk is the best form of nutrition for these babies.
  • If the babies are not able to suck adequately at the breast, then the mother should be encouraged to express her milk regularly for her babies.
  • If she does not have sufficient milk for them, milk from a human milk bank can be used, which is much better for preterm babies than formula milk.

The more stimulation the breasts are given, the more plentiful is the milk supply.

Care of the mother

Involution of the uterus will be slower because of its increased bulk. 'Afterpains' may be troublesome and analgesia should be offered. A good diet is essential, and if the mother is breastfeeding, she requires a high-protein, high-calorie diet. Once the mother is at home she must be encouraged to rest and eat a well-balanced diet. The incidence of postnatal depression has been shown to be significantly higher in twin mothers.

Triplets and higher-order births

A woman expecting three or more babies is at risk of all the same complications as one expecting twins, but more so. She is more likely to have a period in hospital resting before the babies are born and they will almost certainly be delivered prematurely. Perinatal mortality rates are higher for triplets than twins and the incidence of cerebral palsy is also increased. The mode of delivery for triplets or more babies is usually by caesarean section. It is essential that the paediatric team be present. The special dangers associated with these births are:

  • Asphyxia
  • Intracranial injury
  • Perinatal death.

Perinatal mortality and long-term morbidity are both more common among multiple births than singletons. The perinatal mortality rate for twins is about four times that of singletons, and that of triplets 12 times higher.

Embryo reduction

This is the reduction of an apparently healthy higher-order multiple pregnancy down to two or even one embryo so the chances of survival are much higher. The procedure may be offered to parents who have conceived triplets or more. The procedure is usually carried out between the 10th and 12th weeks of the pregnancy. Various techniques may be used, involving the insertion of a needle under ultrasound guidance either via the vagina or, more commonly, through the abdominal wall into the fetal thorax. Potassium chloride is usually used, although some doctors prefer saline. All embryos remain in the uterus until birth.

Selective fetocide

This may be offered to parents with a multiple pregnancy when one of the babies has a serious abnormality. The affected fetus is injected as described in embryo reduction, so allowing the healthy fetus to grow and develop normally.

Further reading

NICE. (2011). Multiple pregnancy: antenatal care for twin and triplet pregnancies. Clinical guideline 129. https://www.nice.org.uk/guidance/CG129

Royal College of Obstetricians & Gynaecologists. Management of monochorionic twin pregnancy. Green-top Guideline No 51. https://www.rcog.org.uk/globalassets/documents/guidelines/t51managementmonochorionictwinpregnancy2008a.pdf

 

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