Rydhström H
Department of Obstetrics and Gynaecology, University Hospital, Lund, Sweden.
Br J Obstet Gynaecol. 1994 Sep;101(9):765-9.
To study the relation between pregnancy loss (one or two fetal deaths in a pair) in twin pregnancy and gender (like-sexed and unlike-sexed pairs), discordant birthweight, and placentation.
The type of placentation for gestations with pregnancy loss was studied, based on material retrieved from the original medical records, for a defined region comprising 20.0% of the total twin population.
Four thousand one hundred and ninety-one unlike-sexed and 10,875 like-sexed twin pairs born in Sweden between 1973 and 1989, in most cases with a gestational duration 28 or more completed weeks.
The relative risk (RR) for pregnancy loss in like-sexed pairs, compared with unlike-sexed ones, was 2.3 and the 95% confidence limits (CL) 1.7-3.1. Not until discordance exceeded 999 g did the pregnancy loss rate for unlike-sexed pairs increase significantly, compared with the (first) stratum with discordance less than 250 g (RR = 6.3; CL 3.5-11.3). For like-sexed twin pairs a higher pregnancy loss rate, compared with the first stratum, was seen already in the stratum with discordance 250-499 g (RR = 1.3; CL 1.0-1.8); a significant increase in pregnancy loss rate was found in all the three strata 500-749 g (RR = 2.1; CL 1.5-3.0), 750-999 g (RR = 3.5; CL 2.3-3.0), and 1000 g or more (RR = 10.9; CL 8.4-14.2), respectively. When calculating the discordance as a percentage of the weight of the larger twin, unlike-sexed pairs experienced a significant increase in pregnancy loss when discordance exceeded 40 to 50%. For like-sexed ones, the corresponding figures were 20 to 30%. In the 47 unlike-sexed pregnancies complicated by pregnancy loss, both twins died in two pregnancies (4.3%), whereas for like-sexed pairs the corresponding figures were 65/279 (23.3%). Of 47 gestations with pregnancy loss in a defined region, 32 were monochorionic (monozygous), nine were like-sexed dichorionic (monozygous or dizygous), and six were unlike-sexed (dizygous).
Pregnancy loss was twice as high in like-sexed compared with unlike-sexed pairs, and only in like-sexed pairs was pregnancy loss strongly correlated to birthweight discordance. In twin pregnancies with one fetal death the risk for the surviving twin to succumb is five to six times higher in like-sexed compared with unlike-sexed pairs and is most probably related to monochorionicity.
研究双胎妊娠中妊娠丢失（一对胎儿中一个或两个死亡）与胎儿性别（同性和异性双胎）、出生体重不一致及胎盘形成之间的关系。
基于从原始病历中获取的资料，对占双胎总数20.0%的特定区域内发生妊娠丢失的妊娠的胎盘形成类型进行研究。
1973年至1989年在瑞典出生的4191对异性双胎和10875对同性双胎，多数妊娠孕周达到或超过28周。
与异性双胎相比，同性双胎妊娠丢失的相对风险（RR）为2.3，95%置信区间（CL）为1.7 - 3.1。直到不一致性超过999 g时，异性双胎的妊娠丢失率才较不一致性小于250 g的（第一）层显著升高（RR = 6.3；CL 3.5 - 11.3）。对于同性双胎，在不一致性为250 - 499 g的层中，与第一层相比妊娠丢失率就已升高（RR = 1.3；CL 1.0 - 1.8）；在不一致性为500 - 749 g（RR = 2.1；CL 1.5 - 3.0）、750 - 999 g（RR = 3.5；CL 2.3 - 5.0）和1000 g及以上（RR = 10.9；CL 8.4 - 14.2）的所有三层中，妊娠丢失率均显著升高。当将不一致性计算为较大胎儿体重的百分比时，异性双胎在不一致性超过40%至50%时妊娠丢失显著增加。对于同性双胎，相应数字为超过20%至30%。在47例并发妊娠丢失的异性双胎妊娠中，有2例妊娠中两个胎儿均死亡（4.3%），而对于同性双胎，相应数字为65/279（23.3%）。在特定区域的47例发生妊娠丢失的妊娠中，32例为单绒毛膜（单卵双胎），9例为同性双绒毛膜（单卵或双卵双胎），6例为异性双绒毛膜（双卵双胎）。
同性双胎的妊娠丢失率是异性双胎的两倍，且仅在同性双胎中妊娠丢失与出生体重不一致密切相关。在有一个胎儿死亡的双胎妊娠中，存活胎儿死亡的风险在同性双胎中比异性双胎高五至六倍，很可能与单绒毛膜性有关。
