[Intrauterine growth characteristics of twins and those twins discordant birthweight].

OBJECTIVE: To investigate the intrauterine growth characteristics of twins and birthweight discordant twins (discordant twins). METHODS: Total of 1010 twin pregnancies (2020 fetuses) with complete delivery records from the Department of Obstetrics and Gynecology, the First and Third Affiliated Hospital of SUN Yat-sen University between January 1, 2000 and July 31, 2010 were studied retrospectively. One handred and ninteen cases (238 fetuses) with intrapair birthweight difference ≥ 25% were determined as the discordant twins group, and the other 891 cases (1782 fetuses) with intrapair birthweight difference < 25% were identified as the concordant twins group. The singleton control group included 4042 singleton pregnancies in the same period. RESULTS: (1) Comparison of clinical data between the twins groups: the birthweight of larger-twin, smaller-twin and intrapair birthweight difference in the discordant twins group and the concordant twins group were (2090 ± 827) g, (1392 ± 592) g, (33.9 ± 9.3)%, and (2408 ± 543) g, (2191 ± 505) g, (8.9 ± 6.5)%, respectively, with significant differences (P < 0.01). The incidence of discordant twins was 11.78% (119/1010). Compared with the concordant twins group, the discordant twins group had higher proportion of monochorionic twins, and higher prevalence of pregnancy complications such as late miscarriage, abnormal umbilical insertion, twin-twin transfusion syndrome and hypertensive disorders in pregnancy (P < 0.05). (2) The characteristics of twin birthweight distribution: 1) In all the 2020 twins, 80.05% (1617/2020) fetuses had birthweight below the 50(th) percentile of the singleton control group, while 23.71% (479/2020) feeuses got birthweight below the 10(th) percentile of the singleton control group. 2) After 19(th) gestational week, the 50(th) and 90(th) percentile of all twins' birthweight were lower than those of singletons. After 38(th) gestational week, the birthweight of singletons kept increasing and reached its peak at 41(th) week, while the birthweight of twins reached its peak at 38(th) week, followed by a decline at 39 weeks, which was even lower than the 10(th) percentile of the singleton control group. 3) The distribution of birthweight of larger- and smaller-twin in the discordant twins group: 65 (54.6%, 65/119) larger-twins and one (0.8%, 1/119) smaller-twin had birthweight above the 50(th) percentile of all twins, while 5 (4.2%, 5/119) larger-twins and 97 (81.5%, 97/119) smaller-twins got birthweight below the 10(th) percentile of all twins. CONCLUSIONS: (1) The patterns of birthweight curves for each gestational week are different between twins and singletons. In order to evaluate the growth of twins, birthweight reference for twins should be employed. (2) According to the reference of twins birthweight, the most discordant twins are complicated with fetal growth restriction at least in one twin.

[Clinical features of abnormal chromosome karyotypes in twin pregnancies complicated with structural abnormalities].

OBJECTIVE: To investigate the clinical features of the abnormal chromosome karyotypes in twin pregnancies complicated with fetal malformations. METHODS: Totally 181 twin pregnancies (362 fetuses) in which one or two fetuses had abnormalities diagnosed by ultrasound were referred to the First Affiliated Hospital of Sun Yat-Sen University from January, 2000 to September, 2010. They were divided into different groups according to (1) maternal age: the cases with maternal age ≥ 35 were divided into advanced pregnancy group (105 fetuses), and those with maternal age < 35 were divided into young pregnancy group (203 fetuses); (2) conceived method: those conceived by assisted reproductive technology were divided into assisted reproductive group (81 fetuses), and the natural conception pregnancies were divided into natural conception group (227 fetuses); (3) chorionicity: the monochorionic twin (MCT) pregnancies were divided into MCT group (123 fetuses), and the dichorionic twin (DCT) pregnancies were divided into DCT group (185 fetuses); (4) structural abnormalities: 205 fetuses with structural abnormalities were divided into the abnormal fetal group, and 103 fetuses without structural abnormalities were divided into the normal fetal group. All fetuses were examined by the ultrasound and chromosomes were examined in 308 fetuses. RESULTS: (1) The karyotype of fetuses: among 181 twin pregnancies, 23 cases had chromosomal abnormalities in 1 or 2 fetuses (12.7%, 23/181), and chromosomes were examined in both fetuses in 20 of 23 cases. Twenty-six of 308 fetuses were found with abnormal chromosomes (8.4%, 26/308), and the aneuploid was the most common type of abnormal karyotypes (53.8%, 14/26). Twenty-one of 205 fetuses with malformations were found with abnormal karyotypes (10.2%, 21/205). (2) Seven of 123 fetuses in MCT group were with abnormal karyotypes (5.7%, 7/123), and 19 of 185 fetuses in DCT group were with abnormal karyotypes (10.3%, 19/185). There was no statistical difference of abnormal chromosome incidence between the two groups. There were 14 fetuses with aneuploid in DCT group (7.6%, 14/185); but there was no fetus with aneuploid in MCT group. There was statistical difference between these two groups. In two cases of DCT group, only one fetus with malformation received chromosome examination because another fetus was dead, and the karyotypes were trisomy 21 and trisomy 18 respectively. Both fetuses of the rest 17 cases received chromosome examination, and the chromosomes of both fetuses in each pregnancy were different. Fifteen of 19 fetuses with abnormal chromosomes in DCT group were complicated with structural abnormalities, and 7 fetuses of 4 twin pregnancies in MCT group were with chromosomal abnormalities. (3) The comparison of the abnormal karyotype incidence between the advanced pregnancy group and young pregnancy group: the abnormal karyotype incidence of the advanced pregnancy group was 7.6% (8/105), and that was 8.9% (18/203) in young pregnancy group. There was no statistical difference between the two groups (P > 0.05). Six of 105 fetuses in advanced pregnancy group were aneuploids (5.7%, 6/105), and 8 of 203 fetuses in young pregnancy group were aneuploids (3.9%, 8/203). The aneuploid incidence in advanced pregnancy group was significantly higher than that in young pregnancy group (P < 0.05).(4) The comparison of the abnormal karyotype incidence between the assisted reproductive group and the natural conception group: 11 of 81 fetuses were with the abnormal karyotypes in assisted reproductive group (13.6%, 11/81), and 15 of 227 fetuses were with the abnormal karyotypes in assisted reproductive group (6.6%, 15/227). There was statistical difference between the two groups (P < 0.05). There were 7 fetuses with the aneuploid in assisted reproductive group (8.6%, 7/81) and 7 fetuses with the aneuploid in natural conception group (3.1%, 7/227), which showed no statistical difference (P > 0.05). (5) The comparison of the abnormal karyotype incidence between the abnormal fetal group and normal fetal group: 21 of 205 fetuses in abnormal fetal group were with abnormal karyotypes (10.2%, 21/205), and 5 of 103 fetuses in normal fetal group were with abnormal karyotypes (4.9%, 5/103). There was no statistical difference (P > 0.05). 13 fetuses in abnormal fetal group were with the aneuploid (6.3%, 13/205), and only one fetus in normal fetal group was aneuploid (1.0%, 1/103). There was statistical difference between the two groups (P < 0.05). CONCLUSIONS: Aneuploid is the most common abnormal karyotype in twin pregnancy complicated with fetal abnormalities, especially trisomy 21. Aneuploid mainly occurs in only one fetus of DCT, and chromosomal discordance is usually found in DCT. While in MCT, the twin fetuses with the same abnormal karyotype may have different phenotypes. The results suggest that it is necessary to analyze both karyotypes of twins even if only one fetus is complicated with structural abnormalities.