MULTIPLE GESTATION
Incidence and epidemiology:Twins account for about 1% of all pregnancies with 80% being dizygotic & 20% monozygotic.The rate of multiple births in USA increased dramatically with the more use of ovulation induction to reach in 2002 to 3% of all pregnancies .
The incidence of DZ twins varies with:
Ethnic group: the spontaneous incidence of twins is greater in Negro race, reaching 1in 30, and lower in Mongol race (1 in 150).
Maternal age: the incidence of twin pregnancies rises slightly with increasing maternal age up to 40. (2% at 35y.) Rising to a peak between 35-39y.
Increasing parity: 2% after 4 pregnancies. A woman who has given birth to twins is 10 times more likely to have a multiple conception in a subsequent pregnancy than a woman who has not previously had twins.
The treatment of anovulation and other causes of infertility ( IUI and IVF ) make an important contribution to the incidence of twinning. Ovulation induction by clomiphene 8% or gonadotrophins 24% -------
Family history: a tendency to multiple pregnancy in inherited and it occurs more frequently in certain families ( Dizygotic twin ).
While the incidence of MZ twins is similar in all ethnic groups and does not vary with maternal age, parity or method of conception.
Varieties of Twins
Twins may be binovular (dizygous) or uniovular (monozygous)Binovular twins (DZ)
Arising from fertilization of two ova from the same or opposite ovaries.Each fetus has its own membranes, chorion and amnion, and its own placenta (dichorionic diamniotic placentation).
When the implantation sites happen to be close together the placentas may become fused, but there is never any anastomosis between their blood vessels.
The fetuses may be similar or different in sex.
Their genetic material will be differ.
This variety of twins is four times more common than the uniovular variety.
Uniovular twins (MZ)
Are developed from a single ovum which after fertilization has undergone division to from two embryos.
When a single embryonic mass splits into 2 within three days of fertilization (occurs in 1/3 of MZ) → each fetus has its own amniotic sac and placenta (diamniotic and dichorionic) they are the same as DZ twins but the fetuses will be identical.
When embryonic splitting after the third day following fertilization → there are vascular communication within the 2 placental circulation (monochorionic diamniotic placentation) this accounts for 2/3 for MZ twins.
Embryonic splitting after the 9th day following fertilization → (monoamniotic monochorionic twins). 1% of MZ.
Splitting after the 12th day → conjoined twins (rare)
Maternal Responses
The physiological response to twin pregnancy may be summarized as:An exaggerated adaptation of all systems and especially of the cardiovascular system.
Cardiac output increase about 20% more than usual increase .
The normal increase in plasma volume during pregnancy is much greater & the normal increase in total circulating red cell mass shows an additional increment of about 250ml.
haematocrite and hemoglobin values are even lower than in singleton pregnancies (because this is not in proportion to the increment in plasma volume)
* Other systems
increase in respiratory tidal volumea higher glomerular filtration rate.
All the changes seem to be due to increase demands to meet the needs of the fetuses cental .
Maternal complications, which result from exaggerated physiological responses to multiple pregnancy, are hyperemesis gravidarum and anaemia.
Diagnosis of twins
Early symptoms of pregnancy such as morning sickness may be more pronounced and pregnancy hypertension is common.
The women may notice an unusual degree of abdominal enlargement and excessive fetal movement.
In late pregnancy she may have discomfort and shortness of breath because of the large size of the uterus.
Anaemia is common. A part from the fact that there is a great increase in plasma volume there is a double fetal demand for iron, megaloblastic anaemia is also common.
oedema of the legs is common and any tendency to haemorrhoid or varicose veins of the legs is accentuated.
On examination
The uterus is found to be larger than expected from the duration of gestation.Polyhydramnios may occur with twins, adding to the size and confusing the diagnosis.
Two fetal heads can be felt.
Both backs and both breeches may be identified and an unusual number of fetal parts.
If heart movements are detected with the U\S in2 separate areas or directions the diagnosis of twins is almost certain.
By U\S scan in early pregnancy to separate gestational sacs can be identified from about the 7th week or sooner. If routine scanning of all women is carried out at 16 weeks twins should rarely be missed.
If antenatal supervision is poor the diagnosis sometimes is missed until delivery, or after the birth of the first twin.
Complications of pregnancy :
preterm labor and birth About half of twins and nearly all higher-order multiples (triplets , quadruplets , etc) are premature (born before 37 weeks). The higher the number of fetuses in the pregnancy, the greater the risk for early birth. Premature babies are born before their bodies and organ systems have completely matured. These babies are often small, with low birthweights (less than 2,500 grams or 5.5 pounds), and they may need help in breathing, eating, fighting infection, and staying warm. Very premature babies, those born before 28 weeks, are especially vulnerable. Many of their organs may not be ready for life outside the mothers uterus and may be too immature to function well. Many multiple birth babies will need care in a neonatal intensive care unit (NICU).
pregnancy-induced hypertension Women with multiple fetuses are more than three times more likely to develop high blood pressure . This condition often develops earlier and is more severe than singleton pregnancy . It can also increase the chance of placental abruption (early detachment of the placenta).
anemia Anemia is more than twice as common in multiple pregnancies as in a single birth.
birth defects Multiple birth babies have about twice the risk of congenital (present at birth) abnormalities including neural tube defects (such as spina bifida), gastrointestinal, and heart abnormalities. This increased risk is limited to identical twins.
IUGR :
Likely to occur due to uterine overcrowding & usually the growth lag is 2 weeks
miscarriage A phenomenon called the vanishing twin syndrome in which more than one fetus is diagnosed, but vanishes (or is miscarried), usually in the first trimester, is more likely in multiple pregnancies. This may or may not be accompanied by bleeding. The risk of pregnancy loss is increased in later trimesters as well.
twin-to-twin transfusion syndrome Twin-to-twin syndrome is a condition that develops only with identical twins that share a placenta. Blood vessels connected within the placenta and divert blood from one fetus to the other. It occurs in about 15 percent of twins with a shared placenta.
abnormal amounts of amniotic fluid Amniotic fluid abnormalities are more common in multiple pregnancies, especially for twins that share a placenta.
cesarean delivery Abnormal fetal positions increase the chances of cesarean birth.
postpartum hemorrhage The large placental area and over-distended uterus place a mother at risk for bleeding after delivery in many multiple pregnancies.
Management of twin pregnancy
Routine antenatal care:
Because of more frequent complications
The first step is to make the diagnosis of multiple pregnancy as early as possible during gestation so that the complications can be detected early.
Visits should be four weekly until 28w, twice weekly to32w, then weekly.
U/S examination plays a major role in management.
In the first trimester it is used to:
Diagnose the number of fetuses
Determine chorionicity
Accurately dating pregnancy
Detect major fetal abnormalities
In the second trimester it is used to detect fetal abnormalities.
In the third trimester to monitor fetal growth and well being.
In labour to determine presentation and position of the fetuses.
General advice should encourage adequate rest, as many women with twin pregnancy will find themselves tired.
The practice of admitting women with twins to hospital from the 30th to the 35th week is now less common, but it may be advisable if the home conditions are poor because rest will increase the placental blood flow and so improve fetal growth and for specific medical indications .
There is no convincing evidence that the prophylactic use of tocolytic drugs or cervical suture will reduce the incidence of preterm labour in twin pregnancy.
We should advice the patient for routine iron and folic acid supplementation.
Management of twin labour and delivery:
In 70% of twin pregnancies the first fetus presents by the vertex. Malpresentations are common, especially of the second twin, but mechanical difficulty is rare, as the fetuses tend to be smaller.The second twin is also more at risk than the first from intrapartum hypoxia. 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.
Labour should be conducted in a well-equipped hospital under the supervision of an experienced obstetrician, with an expert obstetric anaesthetist and a paediatrician in attendance.
The first stage:
Is managed in the ordinary way, labour is no often prolonged and with small fetuses may be rapid.
In early labour an I.V infusion should be setup, to which oxytocin may be later be added if uterine contractions decrease following delivery of the first twin.
Epidural analgesia is useful as it facilitates manipulation of the 2nd fetus.
Fetal heart monitoring should be continued throughout the delivery of both twins. A twin cardiotocography (CTG) machine and portable US machine should be available.
CS might be performed if:
either CTG trace becomes abnormalprolonged delay in the first stage of labour
Both twins were breech presentation or lying transversely or the twins were conjoined.
The second stage:
Is managed in the usual way unless some complications arise.Unless the perineum is very lax, an episiotomy should be performed routinely, under local anaesthesia if an epidural injection has not been given.
Immediately after the delivery of the first twin the abdomen is palpated to determine the lie of the second fetus.
If it is oblique or transverse it is corrected by external version through the lax abdomen to bring one pole of the fetus over the cervix. If this proves difficult internal version and breech extraction should be performed. This is made easier if the second bag of membranes is left intact for as long as possible
Cord prolapse should be excluded and fetal heart monitoring must be continued.
Fetal distress of the second twin may occur because:
The volume of the uterine cavity is reduced after delivery of the first twin.There may be separation of the placenta on which the second twin depends.
Cord prolapse.
Uterine contractions are often stopped for a few minutes after delivery of the first twin. When they start again delivery will occur.
If the uterine contractions does not return within 5 min. after the delivery of the first twin Syntocinon (2 units in500ml glucose solution) should be started to accelerate labour .
The optimum time interval between births is said to be 10-30min.
If fetal distress is noted while the second presenting part remain high, the ventouse is the ideal instrument for the vertex presentation, while breech extraction should be performed if the presentation is podalic.
Third stage of labour:
There is an increase risk of postpartum haemorrhage because of :
The large size of the placental site
Excessive uterine distention with consequent lack of uterine muscle tone.
This risk is minimized by continuous oxytocin infusion through and for some time after the 3rd stage of labour. A prophylactic injection of syntometrine should be given with the birth of the second twin and the placenta delivered in the usual way.
Complications of labour:
malpresentation45% - both presented by head
35% - one head and the other by breech
10% - both by breech
10% - transverse lie is associated with a cephalic or a breech presentation.
Very rarely for both fetuses to lie transversely.
postpartum haemorrhage
cord prolapse
Locked twins. This is a very rare complication occurring in less than 1 in 1000 twin deliveries. Locking may occur when the first twin presents as a breech and the second as a vertex. The after coming head of the first twin is caught above the chin of the second twin. CS and delivery of the second twin from above is probably the easiest course.
Caesarean section
Elective CS has a place in twin delivery if:
The pregnancy is complicated by severe hypertension
The woman is old or have a bad obstetrical history
The leading twin presents by the breech or transverse lie
Preterm labour before 34w
Previous CS
In the presence of a previous lower segment CS the contraindications for trial of vaginal delivery are the same as in singleton, but there are two anxieties about previous Cs in women with twins
over distension of the uterus can lead to excessive thinning of the scar and to its dehiscence
a need to manipulate the second twin at delivery might cause scar dehiscence or rupture .