Perinatal outcome of twins in relation to chorionicity.PA Hatkar, AG Bhide
Nowrosjee Wadia Maternity Hospital, Parel, Mumbai, India., India
Twin gestation, a high-risk pregnancy is responsible for 10% of all perinatal mortalities. The high perinatal mortality of twins has been repeatedly stressed over the years. Studies have also revealed difference in the perinatal mortality rates in relation to chorionicity. Thus, a prospective study of 100 twin pregnancies was carried out at our institute to assess the morbidity and mortality of twins in relation to chorionicity and to analyse the factors responsible for the greater loss. The perinatal mortality rate of monochorionic twins was 17.64% and that of dichorionic twins was 8. 88%, which is statistically significant. Birth weight was found to be the most important factor correlating with mortality rates. The higher perinatal mortality of monochorionic twins was largely due to low birth weights (29.3% of monochorionic twins weighed less than 1500 gm as compared to 12.6% of dichorionic twins). Avoidable deaths were comparable in the two twin groups but dichorionic twins showed greater percentage of fresh stillbirths (40%) whereas in monochorionic twins, 50% were macerated stillbirths. Prematurity was another common factor responsible for greater perinatal mortality in monochorionic twins. Monochorionic twins showed increased incidence of discordant growth (34.8%) as compared to that of dichorionic twins (14.08%). The type of placentation did influence the perinatal outcome of twins making its antenatal diagnosis important.
Keywords: Birth Weight, Comparative Study, Female, Gestational Age, Human, Pregnancy, Pregnancy Outcome, Prospective Studies, Twins, Dizygotic, Twins, Monozygotic,
Few topics in obstetrics have stimulated more interest and generated more literature than multiple gestation. Twin pregnancies are associated with significantly higher morbidity and mortality than are sigleton pregnancies. (Five-fold higher according to Botting BJ et al and six-fold higher according to Brian J. McCarthy).
Studies have also been done to correlate the type of placentation with incidence of perinatal mortality. Potter in his study has shown that twins with monochorionic placentas had a higher perinatal mortality (13.2%) than twins with dichorionic placentas (9.6%).
A prospective study of 100 twin pregnancies was carried out at our institute, which aimed:
1. To assess the morbidity and mortality of twins in relation to chorionicity.
2. To analyse factors responsible for the greater loss.
A prospective study and retrospective analysis of 100 twin pregnancies was carried out. Data was collected during antenatal period and delivery of the patient and neonatal course of the babies was followed up. The population came from a largely illiterate lower to middle socio-economic strata.
The data was analysed with reference to the following variables and the perinatal outcome was studied :
The number of dizygous twins in any population is twice the number of twins of different sex, the remainder being monozygous (Weingberg's rule, 1903). In the present study, Weingberg's rule was applied for determination of number of monozygous and dizygous twins.
* Type of placentation
* Maternal age (in years)
* Parity (defined as the number of previous viable births in this report)
* Gestational age
* Birth weight (in grams)
* Type of presentation of twins
* Mode of delivery
* Stay in Neonatal Intensive Care Unit (NICU)
* Discordant growth.
Perinatal mortality is defined as the number of stillbirths plus neonatal deaths within seven days per 1000 births (excluding macerated still births). Thus, perinatal mortality rate was calculated as follows:
Macerated still births + Fresh still births + Neonatal deaths
Total number of twins - Number of stillbirths
In the present population, the estimated number of monozygotic twin pairs was 32 and that of dizygotic twin pairs was 68.
Thus, 32% of the present population were monozygotic twins and the remaining 68% were dizygotic twins.
Type of placentation
The type of placentation was determined at the time of delivery. The two principally different placental types found were monochorionic and dichorionic.
In the present population, the number of monochorionic diamniotic twins was 29 (29%), that of dichorionic diamniotic twins was 71(71%) and there was not a single monochorionic monoamniotic twin pair.
In the present study of 100 twin pregnancies, out of 200 babies delivered, 6 were macerated stillbirths, 8 were fresh stillbirths and 7 were neonatal deaths. Overall, perinatal mortality was 21 out of 200. Thus, overall perinatal mortality rate was 112.90/1000 twin births.
The perinatal mortality rate of monochorionic and dichorionic twins in our study was calculated to be 176.47/1000 twin births and 88.88/1000 twin births respectively.
Thus, perinatal mortality rate of monochorionic twins was 17.64% and that of dichorionic twins was 8.88%.
[Table - 1] shows the perinatal outcome of monochorionic and dichorionic twins.
Perinatal outcome of monochorionic and dichorionic twins in relation to their birth weights is shown in [Table - 2].
Average birth weight of monochorionic twins = 1663.80 gms
Average birth weight of dichorionic twins = 2059.15 gms
At the birth weights less than 1500 gms, the number of monochorionic twins was greater than dichorionic twins and vice versa.
Critical weight and avoidable deaths
In our study, 999 gms has been taken as critical weight below which mortality is mainly due to prematurity, all other factors being secondary to prematurity. Above this critical weight, all perinatal mortalities were considered "Avoidable deaths".
Out of 21 perinatal mortalities, 14 were avoidable deaths of which 4 were monochorionic twins (6.8%) and 10 were dichorionic twins (7.04%)
The mean maternal age in monochorionic twins was 23 years (20-24 years) and in dichorionic twins was 24 years.
The number of monochorionic and dichorionic twins was comparable in relation to parity.
[Table - 3] gives the gestational age in relation to 100 twins gestations.
The average gestational age for monochorionic twins was 35.5 weeks and that for dichorionic twins was 35.7 weeks. Majority of the twins delivered around 34-37 weeks.
Type of presentation
[Table - 4] shows the various types of presentations in 100 twins gestations. Majority of the monochorionic and dichorionic twins presented as vertex-vertex.
Mode of Delivery
The various modes of delivery in monochorionic and dichorionic twins are outlined in [Table - 5].
29.3% of monochorionic twins required LSCS whereas 34.50% of dichorionic twins had to be delivered by LSCS.
[Table:6] represents the duration of NICU stay in monochorionic and dichorionic twins.
Out of 58 monochorionic twins, 49 were born alive and 24 were transferred to the Neonatal Intensive Care Unit at birth. Only two of them died due to low birth weight and the rest 22 of them went home alive.
Discordant growth causes a difference in the weight of the twins. This difference is expressed as a percentage of the larger twin's weight and a discrepancy of 20% or more is significant.
Some classified discordant twins in two categories according to the discrepancy in their birth weights. Difference in birth weights of 15% to 25% is classified as Grade I and any discordancy greater than 25% as Grade II.
In the present study, 34.48% of monochorionic twins showed discordant growth (Grade I), out of which 3.4% had severe discordancy (Grade II) (twin gestations with one fetal demise were excluded). 14.8% of dichorionic twins had discordant growth (Grade I) but none had severe discordancy (Grade II).
Twin pregnancy opens a fertile field for discussion and study of all obstetric complications that can occur in a single patient. The simultaneous birth of two infants presents formidable hazards to the fetuses.
Dizygotic twins account for two thirds of all twins and one third are monozygotic. Our study obtained comparable [figures]. The incidence of monochorionic placentation in our study was in comparison with Ruhle et al (33%). In our study, the incidence of monochorionic and dichorionic twins did not differ in relation to maternal age and parity. Chorionicity did not influence the type of presentation and LSCS rate.
Perinatal mortality is considered to be the best indicator of obstetric care received by the patient. The perinatal mortality rate of monochorionic diamniotic twins is about 25% and that of dichorionic twins is the lowest, about 9%, which in our study was 17.64% and 8.88% respectively.
Birth weight was found to be the most important factor correlating with mortality rates. Dichorionic twins were heavier than monochorionic twins as evident from the difference in their average birth weights. Blecker and Hemrika had obtained similar results in their study. Also, 29.3% of monochorionic twins had birth weights < 1500 gms of which 20.6% were premature. In comparison, only 12.6% of dichorionic twins had birth weights < 1500 gms of which 9.1% were premature. Thus, low birth weights were indicators of prematurity and/or intrauterine growth retardation. The higher perinatal mortality of monochorionic twins was largely due to low birth weights. In our study, avoidable deaths in monochorionic twins were comparable to those in dichorionic twins. But dichorionic twins showed greater percentage of fresh stillbirths (40%) and monochorionic twins, of macerated stillbirths (50%).
Another factor commonly affecting perinatal outcome of twins was prematurity. Prematurity did account for increased perinatal mortality in extremely premature monochorionic twins as compared to dichorionic twins.
Monochorionic twins showed increased incidence of discordant growth (34.48%) as compared to that of dichorionic twins (14.08%) 3.4% of monochorionic twins showed severe discordancy probably as a result of twin-to-twin transfusion syndrome, which, also resulted in increased incidence of macerated still births in monochorionic twins.
The neonatal morbidity can be roughly assessed by the duration of NICU stay. The percentages of monochorionic and dichorionic twins transferred to NICU were comparable. But four (6.89%) of monochorionic twins had longer stay in NICU (> 30 days) as compared to only 1(1.75%) of dichorionic twins. Neonatal morbidity was seen in the form of asphyxia, hyaline membrane disease, chronic respiratory disease, neonatal depression, neonatal infection, hyperbilirubinaemia, intraventricular haemorrhage in a few cases, etc.
Thus, it can be concluded that perinatal outcome of twins is influenced by the type of placentation. Antepartum diagnosis of the type of placentation would help in identifying the twins at risk for twin-to-twin transfusion syndrome, discordant growth, and thus associated with greater perinatal mortality. Identifying twins with severe discordancy antenatally would also help to decrease the perinatal mortality by ensuring good antenatal care, strict intrapartum monitering and experienced obstetricians to conduct the delivery with good neonatal intensive care.
The authors thank the Dean, Dr. (Mrs.) Vandana R. Walvekar for granting permission to publish the data from Nowrosjee Wadia Maternity Hospital.
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]