Multifetal Pregnancy
Definition :The simultaneous presence of more than one embryo ( most commonly 2 , what is known as twin ) despite the site of implantation . Some cases are heterotopic ( one intrauterine and the other is extrauterine ) or both may be ectopic .
Types :
I- Monozygotic : ( identical or Homologous ) :* Occurs when one ovum fertilized by one sperm spilt to 2 or more parts in early stages of development .
* The results of splitting will depend on the timing of splitting :
1. If splitting occurs in the 1st 72 hours after fertilization ( before inner and outer cell mass differentiation ) , there will be 2 or more fetuses , each one has its own amnion and chorion ( but the placenta may be fused ) .
2. If splitting occurs between the 4th and the 7th day the chorion will be one ( resulting in single placenta ) .
3. If splitting occurs on the 8th day monoamniotic , monochorionic identical twins will result .
4. If splitting occurs after the 8th day if will be incomplete leading to conjoined twins .
* Monozygotic twins are of the same sex , same morphological features , psychological and mental profile and HLA typing . However they are different in :
1. Finger prints . 2. iris pattern . 3. voice .
* In cases of monochrionic twins , the placental circulation may be common for both leading to extensive vascular connection .
II- Dizygotic twins ( fraternal or heterologous ) :
* These results from 2 or more ova fertilized by 2 or more sperms leading to coincidental presence of 2 or more pregnancy sacs .* The mechanisms by which binovular twins occur are :
1. Superfecundation : Fertilization of 2 separate ova from one cycle by 2 sperms in 2 acts of coitus . This mechanism occurs in human .
2. Superfetation : Fertilization of 2 ova from 2 cycles. This mechanism doesnt occur in humans since the occurrence of pregnancy suppresses ovulation .
* Each fetus has its own amnion , chorion , sex and morphological features as any sisters or brothers . Vascular placental connections are rare .
Incidence :
1. Dizygotic twins ( from 2 ova ) : Hellin put an equation that determine the incidence as follows : twin is 1/80 , triplets ( 3 fetuses ) 1/802 , quadruplets ( 4 fetuses ) 1/803 , Quandiplet ( 5 fetuses ) 1/804 , sextuplet ( 6 fetuses ) 1/805 , septuplet ( 7 fetuses ) 1/806 etc . the maximum record number is 15 fetuses . However , these incidences are fasle because in some cases , one embryo dies and is absorbed or expelled with an attach of bleeding in early pregnancy while the other will continue as a singleton pregnancy .
2. Monozygotic twins : More or less fixed incidence throughout the world ( 3.5 7 % ) .
Etiology :
1. Dizygotic twins : The following factors are known to increase the incidence :a. Increased maternal age .
b. Increased maternal parity .
c. Tall and heavy mothers .
d. There is a well-known , but ill-defined familial tendency to dizygotic twining . Racial factors are also considered ( highest in negros and lowest in Japanese ) .
e. Women with higher levels of endogenous FSH ( have also familial tendency ) .
f. Gonadotrophic stimulation of multiple ovulation causes dizygotic twinning .
g. ET of more than one zygote in the IF program .
2. Monozygotic twins : No definite cause is identified and although some incidental cases occur in some families , yet this type is not considered familial . Also , experimental production of uniovular twins is possible when the inner cell mass is opposite to the implantation pole .
Determination of Zygosity :
1. If the sex is different then they must be dizygotic . In general , the male sex decrease as the number of fetuses increase . This may be due to :a. The natural survival is with female sex .
b. XX zygotes tend to split than XY ones .
2. If the are monochorionic and / or monoamniotic , they must be monozygotic .
3. In other cases , zygosity is determined by examination of genetic markers in the various blood groups placental or blood enzymes . Finger and palm printing can also be used . Although each member of a pair of monozygotic twins does not have exactly the same prints , the pattern is similar .
Vascular Connection ( Twin to twin transfusion ) :
Occurs commonly in monochorionic twins and rare in dichorionic type and in dizygotic twins .
Connection may be artery to artery , vein to vein and artery to vein which is the dangerous one because this will lead to pumping of blood from one to the other .
The donor fetus will be smaller , growth retarded , anemic , with organm hypoplasia , low CO , hypovolemia , oliguria and oligohydramnios . Death of this fetus may occur in utero followed by compression by the growing other twin ( called fetus compressus ) or mummification ( fetus papyraceous ) leading to serious coagulopathy to the other fetus . However postnatal prognosis is relatively good .
The recipient fetus will be larger , with accelerated growth , hypervolemic . poplycythemic , with organomegaly , polyuria and polyhydramios . After delivery , death is commonly due to HF . Also hyperbilirubinemia and kernicterus are common .
So , the significance of vascular connection between fetuses are :
1. Early clamping of the cord of the 1st one without milking .
2. Fetus acardiacus : One parasitic fetus is without heart depends on the other's heart . All it is tissues are distorted and rudimentary .
3. Twin to twin transfusion ( TTTT ) leading to :
a. Androgenization of the female fetus .
b. Chimersim ( see endocrinology ) .
c. Death of both as one is over transfused ( HF ) and one is under transfused ( severe IUGR ) .
d. If one died , this increases the risk of DIC in the other .
Maternal Adaptation :
1. Greater weight gain even in the first trimester due to water retention .2. Greater expansion of plasma volume ( combined birth weights correlate with the amount of plasma volume ) . This will result in more physiologic anemia ( although the RBCs mass is greater than singleton pregnancy ) so that 10g% Hb is quit normal by 30 weeks gestation .
3. Greater CO and the blood pressure is slightly lower in midtrimester .
4. Higher erythrocytes sedimentation rate and more increase in leukocytes .
5. Higher total intravascular mass of proteins .
6. Increased glomerular filtration rate .
7. Increased respiratory tidal volume .
8. Increased production of about 50% above normal singleton values of estrogens , progesterone, SP1 , PAPP-A , PP5 , hPL , and alpha-fetoprotein ( controversial ) .
9. The maternal response to higher multiple pregnancies is even greater ; for example , in quadruplet , the plasma volume increases to double that in singleton pregnancies and 50% more than in twin pregnancies .
Complications :
Maternal :
I- During pregnancy :
1. Anemia : Due to increased requirements and plasma expansion .
2. Preterm delivery ( 33% of monozygotic & 25% in dizygotic ) due to :
a. Increased incidence of PROM specially in monozygotic type ( twice the dizygotic ) .
b. Increased uterine distension .
c. Higher risk for associating PIH .
3. Increased risk of PIH ( 45% ) .
4. Antepartum hemorrhage .
a. Large placenta encroaching on the LUS leading to premature separation .
b. Accidental hemorrhage due to higher incidence of associating PIH .
5. Polyhydramnios ( 5 10 % ) .
6. Increased incidence of abortion ( 30% ) : Although it may be more common , it is difficult to determine except in cases who experience disappearing twin after diagnosis of twin pregnancy .
7. Increased risk of malpresentations and malpositions .
8. Maternal distress due to oversized abdomen .
II- During labor :
1. Prolonged labor with maternal and fetal distress .2. Obstructed labor with the resultant rupture of the uterus . Obstructed labor may occur due to malpresentations . fetopelvic disproportion or very rarely ( 1/800 ) locked twins which is a condition in which the head and neck of the 1st twin ( breech ) are locked in the head and neck of the 2nd ( cephalic ) .
3. Retained second twin .
4. Increased incidence of cord prolapse .
5. Increased risk of IAL .
6. Increased risk of operative delivery .
7. Increased risk of maternal genital lacerations .
8. Increased risk of postpartum hemorrhage .
III- During puerperium :
1. Increased risk of deficient lactation .
2. Increased risk of puerperal infections .
Fetal :
1. Higher incidence of IUGR : Due to relatively deficient resources which may affect one partner than the other . This disparity in weight is more evident with monozygotic twin due to shared placenta . However , the state of intrauterine hypoxia leads to enhancement of lung maturity and so RDS is rare ( L/S ration was found to be 5 in a baby weighting 860 g ) .2. Higher incidence of prematurity .
3. Higher incidence of asphyxia .
4. Higher incidence of birth trauma .
5. Higher incidence of postnatal infections .
6. Higher incidence of congenital abnormalities . The incidence in monozygotic twin pregnancies is twice that in dizygotic .
Diagnosis :
I- History :1. Family history of twining .
2. History of induction of ovulation .
3. Overdistension of the abdomen .
II- Examination :
1. Overdistension of the abdomen .
2. Multiple fetal poles ( at least 3 poles are felt ) .
3. FHS are heard at 2 maximum points with 10 beats / min differences .
4. Galloping may be heard due to overlapping of the 2 FHS ( Arnaux sign ) .
III- Special investigations :
1. U/S :
a. Detects 2 distinct sacs as early as 7 Ws gestation .
b. Detects 2 hearts at 14 Ws gestation .
c. With expert sonographer , 20 or more amniotic sacs can be determined .
2. Doppler velocimetry : By depiction of 2 separate sounds as early as 12 Ws .
3. Radiography : Detects fetal skeleton as early as 16 Ws . However , it is no better than U/S besides the potential hazards of indications .
Prophylaxis :
1. Proper use of ovulation drugs .2. Embryo reduction after ET .
Treatment :
I- During pregnancy :1. More frequent antenatal visits to follow up maternal and fetal conditions . Hospitalization is mostly not required .
2. The women should be encouraged to take as much rest as possible at home .
3. Although some authors recommend supplemented diet , the diet of any singleton pregnancy is enough . No additional trace element or vitamin supplementations need to be added to the ordinary mixed diet .
4. Prevention of preterm labor :
a. More rest .
b. No intercourse .
c. Tocolytics ( Yutopar ) .
d. Some recommend routine cerclage .
5. Prevention of PIH :
a. More rest .
b. Less salt in the diet .
c. Low dose aspirin .
6. Post is difficult to deal with in twin pregnancy because it is not possible to assess the condition of both babies . In view of this , it is commonly believed that twin pregnancies should not go beyond 40 weeks .
7. Antepartum fetal surveillance for IUGR and TTTT .
8. Prenatal diagnosis of congenital anomalies . If amniocentesis is indicated , you should determine which sac is samples to avoid double sampling of the same sac . This can be avoided by injecting few ml of indiogcarmine after sampling of the 1st sac to mark it and avoid resampling .
9. Proper management for any complication if occurred .
II- Labor ( Obstetrician , anesthetist & pediatrician ) :
* Method of delivery : The rule is vaginal delivery , but CS indicated in :
1. Non cephalic 1st twin . Some authors report safe vaginal delivery for both breech twins .
2. Retained living 2nd twin .
3. Conjoint twins with hope of treatment .
4. More than twin pregnancy specially quadruplets or more .
5. Fetal age is 28 34 Ws .
6. Other indication for action .
* Management of vaginal delivery :
1. First stage :
a. Partogram with continuous fetal monitoring is mandatory .
b. Oxytocin is usually needed excepted if C/I .
c. Adequate sedation must be provided and this is commonly carried out with epidural anesthesia .
d. More rest and no high enema to avoid PROM .
e. Antibiotics after ROM .
f. Other measures as normal labor .
2. Second stage :
* The 1st fetus is cephalic in 80% ( longitudinally in 99% ) of cases so its delivery is usually easy , but you must divide its cord between 2 clamps .
* After delivery of the 1st fetus , the uterus usually takes a short period of rest before it regains its contractions . During this period , examine the lie of the 2nd fetus .
a. If longitudinal , rupture the membranes and leave it for spontaneous delivery .
b. If oblique or transverse , correct by external cephalic ( or podalic ) versions and then rupture the membranes .
* Delivery of the 2nd twin is usually easy as it is small and the passages are dilated by the 1st one .
* If there is any delay in the onset of uterine contractions , oxytocin drip should be used . If the delivery of the 2nd fetus is delayed more than 1/2 an hour or if fetal distress occurs , extract the fetus immediately according to the following lines :
a. Forceps if the head is engaged .
b. Internal podalic version followed by breech extraction if the head is not engaged or shoulder presentation .
c. Breech extraction if it is breech .
* An undiagnosed second twin is at considerable risk , particularly if an oxytocic drug has been given after the delivery of the first twin . As soon as the diagnosis is made , the lie is checked and the membranes ruptured . The second twin is then delivered as soon as possible .
* Management of locked twins : Try disimpaction under anesthesia . If failed , sacrifiee the 1st fetus which is usually dead by decapitation to deliver the 2nd followed by delivery of the head of the 1st .
* Management of conjoined twins ( very rare ) : CS is done if there is hope for life otherwise deliver vaginally after destructive operation ( it available ) .
N.B.
Delay of delivery of the 2nd twin over one hour may cause .
a. Reformation of the cervix .
b. Prolapse of the cord .
c. Remature separation of placenta .
d. Intra-aminotic infection .
3. Third stage :
* There may be one or 2 placentae . The usual method of delivery is the active method by giving ergometrine after delivery of the 2nd twin . Occasionally , the first placenta is delivered before the second twin .* Careful observation for post-partum hemorrhage .
Prognosis :
The perinatal mortality in twins is about 5 6 times higher than in singletons and the perinatal mortality in monozygotic is higher than in dizgyotic twins .The main cause of death is low birth weight due to both growth retardation and preterm labor .
Male twins are at greater risk than females and the second twin has a worse prognosis than the first .
Second twins tend to have a lower Apgar score than do first twins .