妊婦の血小板減少について

論文

N Engl J Med 2018;379:32-43.
Platelet Counts during Pregnancy

Clinical question

妊婦は希釈などによる血小板は当然減少する.どの程度までの減少は許容されるんだろうか.

Key point

妊娠中に血小板が10万を下回る時は原因を精査するべし.

Abstract

背景

合併症を有しない妊娠中の女性の血小板数が 150,000/mm3 未満で,ほかに原因が特定されなければ,妊娠性血小板減少症とされる.妊娠に関連する合併症を有する女性では,血小板数がさらに少ない可能性がある.しかし,妊娠中の血小板減少症の発症と重症度は明確にされていない.

方法

2011~14 年にオクラホマ大学医療センターで出産した女性の妊娠中の血小板数を評価した.妊娠女性の血小板数を,1999~2012 年に全米健康栄養調査(NHANES)に参加した非妊娠女性の血小板数と比較した.

結果

調査期間中に発生した出産 15,723 件のうち,7,351 例の女性が解析に十分なデータを有していた.このうち 4,568 例が合併症を有さず,2,586 例が妊娠に関連する合併症を有し,197 例が血小板減少症に関連する既存疾患を有していた.合併症を有しない妊娠女性において,妊娠第 1 三半期(平均妊娠週数 8.7 週)の平均血小板数は 251,000/mm3 であり,非妊娠女性 8,885 例の平均血小板数(273,000/mm3)よりも少なかった(P<0.001).出産時には,合併症を有しない妊娠女性の 9.9%で血小板数が 150,000/mm3 を下回った.合併症を有しない妊娠・出産の期間中に,血小板数が 100,000/mm3 を下回ったのは 45 例(1.0%)のみであった.血小板数が 80,000/mm3を下回った合併症を有しない妊娠女性 12 例のうち,診療録の再評価によりほかに血小板減少症の原因がないと確認されたのはわずか 5 例(0.1%, 血小板数範囲 62,000~78,000/mm3, 中央値 65,000/mm3)であった.出産時に血小板数が 150,000/mm3 未満であった割合は,妊娠に関連する合併症を有する女性のほうが,合併症を有しない妊娠女性よりも高かった(11.9% 対 9.9%,P=0.01).妊娠に関連する合併症を有する女性のうち,59 例(2.3%)が妊娠・出産の期間中に血小板数が 100,000/mm3 を下回り,31 例(1.2%)は 80,000/mm3 を下回った.

まとめ

調査した女性全体において,平均血小板数は妊娠中に減少し,減少は妊娠第 1 三半期に始まった.血小板数が 100,000/mm3 未満の女性では,妊娠またはその合併症以外の原因を検討すべきである.(米国国立心臓・肺・血液研究所から研究助成を受けた.)

英単語

Table and Figure

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原文

BACKGROUND
Platelet counts of less than 150,000 per cubic millimeter during uncomplicated pregnancies are described as gestational thrombocytopenia if no alternative cause is identified. Platelet counts may be even lower in women with pregnancy-related complications. However, the occurrence and severity of thrombocytopenia through- out pregnancy are not defined.
METHODS
We evaluated platelet counts throughout pregnancy in women who delivered at Oklahoma University Medical Center between 2011 and 2014. These platelet counts were compared with those of nonpregnant women who were included in the Na- tional Health and Nutrition Examination Survey from 1999 through 2012.
RESULTS
Among the 15,723 deliveries that occurred during the study period, 7351 women had sufficient data for our analyses. Of these women, 4568 had uncomplicated pregnancies, 2586 had pregnancy-related complications, and 197 had preexisting disorders associated with thrombocytopenia. Among the women who had uncom- plicated pregnancies, the mean platelet count in the first trimester (mean gesta- tion, 8.7 weeks) was 251,000 per cubic millimeter, which was lower than the mean platelet count in the 8885 nonpregnant women (273,000 per cubic millimeter) (P<0.001). At the time of delivery, 9.9% of the women with uncomplicated preg- nancies had a platelet count below 150,000 per cubic millimeter. During the course of the uncomplicated pregnancies and deliveries, only 45 women (1.0%) had a platelet count below 100,000 per cubic millimeter. Among the 12 women with uncomplicated pregnancies who had a platelet count below 80,000 per cubic mil- limeter, only 5 (0.1%, among whom the range of platelet counts was 62,000 to 78,000 per cubic millimeter; median, 65,000) were identified by medical record review as having no alternative cause for the thrombocytopenia. Platelet counts of less than 150,000 per cubic millimeter at the time of delivery were more common among women who had pregnancy-related complications than among women who had uncomplicated pregnancies (11.9% vs. 9.9%, P=0.01). Throughout their preg- nancies and deliveries, 59 women (2.3%) with pregnancy-related complications had a platelet count below 100,000 per cubic millimeter, and 31 (1.2%) had a platelet count below 80,000 per cubic millimeter.
CONCLUSIONS
Mean platelet counts decreased during pregnancy in all the women, beginning in the first trimester. In women who have a platelet count of less than 100,000 per cubic millimeter, a cause other than pregnancy or its complications should be considered. (Funded by the National Heart, Lung, and Blood Institute.)

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