新華社倫敦8月7日電俗話說“懷胎十月”,，然而由于人類的個體差異等原因,，這并不是一個普遍準確的預產(chǎn)期,。一項最新研究顯示，女性孕期時間彼此之間的正常差異可達5周,。
英國《人類的繁衍》雜志7日刊載一份美國研究報告稱，女性的預產(chǎn)期一般被定為其最后一次月經(jīng)后第280天,，但其實僅有4％的孕婦會在當天生產(chǎn),，在預產(chǎn)期前后10天內(nèi)生產(chǎn)的約占七成,。
美國國家環(huán)境衛(wèi)生科學研究所對125名懷孕女性進行了跟蹤調(diào)查，研究人員利用新技術對這些女性受孕的確切時間及分娩時間進行分析后發(fā)現(xiàn)，她們的懷胎時間從35周到40.5周不等。這項研究排除了早產(chǎn)等影響孕期時間的狀況,，受調(diào)查的女性都是正常生產(chǎn)。
這項研究還發(fā)現(xiàn),，孕期時間與孕婦一系列自身因素相關，比如年齡較大的孕婦孕期較長,，自己出生時體重較大的女性往往會孕期長，而前一次懷孕時孕期長的,，再次懷孕仍會有較長的孕期,。
研究人員說，此前人們就知道女性的孕期有個體差異,，本次研究為分析這種差異提供了具體的數(shù)據(jù)支撐,，結(jié)果顯示正常孕期差異可達5周之多。研究人員指出,，醫(yī)生在為孕婦估算預產(chǎn)期的時候,，應該考慮個體差異的影響。（生物谷 Bioon.com）
生物谷推薦的英文摘要
Human Reproduction doi: 10.1093/humrep/det297
Length of human pregnancy and contributors to its natural variation
A.M. Jukic, D.D. Baird, C.R. Weinberg, D.R. McConnaughey andA.J. Wilcox.
STUDY QUESTION How variable is the length of human pregnancy, and are early hormonal events related to gestational length?
SUMMARY ANSWER Among natural conceptions where the date of conception (ovulation) is known, the variation in pregnancy length spanned 37 days, even after excluding women with complications or preterm births.
WHAT IS KNOWN ALREADY Previous studies of length of gestation have either estimated gestational age by last menstrual period (LMP) or ultrasound (both imperfect measures) or included pregnancies conceived through assisted reproductive technology.
STUDY DESIGN, SIZE, DURATION The Early Pregnancy Study was a prospective cohort study (1982–85) that followed 130 singleton pregnancies from unassisted conception to birth, with detailed hormonal measurements through the conception cycle; 125 of these pregnancies were included in this analysis.
PARTICIPANTS/MATERIALS, SETTING, METHODS We calculated the length of gestation beginning at conception (ovulation) in 125 naturally conceived, singleton live births. Ovulation, implantation and corpus luteum (CL) rescue pattern were identified with urinary hormone measurements. We accounted for events that artificially shorten the natural length of gestation (Cesarean delivery or labor induction, i.e. ‘censoring’) using Kaplan–Meier curves and proportional hazards models. We examined hormonal and other factors in relation to length of gestation. We did not have ultrasound information to compare with our gold standard measure.
MAIN RESULTS AND THE ROLE OF CHANCE The median time from ovulation to birth was 268 days (38 weeks, 2 days). Even after excluding six preterm births, the gestational length range was 37 days. The coefficient of variation was higher when measured by LMP (4.9%) than by ovulation (3.7%), reflecting the variability of time of ovulation. Conceptions that took longer to implant also took longer from implantation to delivery (P = 0.02). CL rescue pattern (reflecting ovarian response to implantation) was predictive (P = 0.006): pregnancies with a rapid progesterone rise were longer than those with delayed rise (a 12-day difference in the median gestational length). Mothers with longer gestations were older (P = 0.02), had longer pregnancies in other births (P < 0.0001) and were heavier at birth (P = 0.01). We did not see an association between the length of gestation and several factors that have been associated with gestational length in previous studies: body mass index, alcohol intake, parity or offspring sex.
LIMITATIONS, REASONS FOR CAUTION The sample size was small and some exposures were rare, reducing power to detect weak associations.
WIDER IMPLICATIONS OF THE FINDINGS Human gestational length varies considerably even when measured exactly (from ovulation). An individual woman's deliveries tend to occur at similar gestational ages. Events in the first 2 weeks after conception are predictive of subsequent pregnancy length, and may suggest pathways underlying the timing of delivery.
STUDY FUNDING/COMPETING INTEREST This research was supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences. None of the authors has any conflict of interest to declare.
