Women who are stressed while trying for a baby are more likely to have girls, research suggests.
A study found that those who were under pressure at home, work or in their love life in the weeks or months before becoming pregnant had higher than usual odds of giving birth to a daughter rather than a son.
The finding, by Oxford University and US researchers, means the economic downturn could see more women give birth to daughters. The study follows others that have shown the number of baby boys goes down following major upheavals.
For instance, in the months after the 9/11 terrorist attacks, the number of boys born in New York plunged, while the economic chaos that followed the collapse of the Berlin Wall saw far fewer boys born than expected in the former East Germany in 1991.
But the latest study is the first to link the phenomenon to the stresses and strains of everyday life and to rising levels of stress hormones.
Some 338 women from around the UK who were trying to get pregnant kept diaries about their lives and sex lives and filled in questionnaires about how stressed they felt. Levels of stress hormones including cortisol were measured in the months before pregnancy.
Of the babies born, 58 were boys and 72 were girls. Normally, in Britain 105 boys are born for every 100 girls.
The most stressed women were up to 75 per cent less likely to have boys than the least stressed, the conference in Orlando, Florida, was told. Cortisol levels rise when people suffer long-term stress such as pressure at work and bad relationships.
It isn't known why high levels of cortisol appear to cut the odds of having a boy.
The gender of a baby is determined by the chromosomes in the father's sperm and so is set at conception.
But it is possible that high levels of cortisol somehow make it more difficult for male embryos to implant in the womb.
In addition, male babies may be more fragile and so more likely to be miscarried when cortisol levels are high, leading to more girls being born.


据英国《每日邮报》10月17日报道，研究表明，女性在计划怀孕产子时如果承受较大的压力，更有可能怀上女孩。
一项研究发现，那些在怀孕前处于家庭、工作或者感情生活压力下的女性，怀上女孩的几率比男孩大得多。


牛津大学和美国研究人员的这一发现意味着，在经济衰退时期，会有更多的女性产下女婴。在此之前，已有其他研究表明，在经历大的社会动乱之后新生男婴的总数会有所下降。

比如，在9·11恐怖袭击后的数月内，纽约出生的男婴数量下降。而在柏林墙倒塌后引起的经济萧条时期，1991年东德出生的男婴比预期的少得多。


但这项最新研究还是第一次将这种现象与日常生活的紧张压力以及增长的应激激素水平相联系。

英国各地大约338名打算怀孕的女性以日记形式记录了她们的日常活动和性生活，然后填写了调查问卷，问卷内容是关于她们所感受到的压力大小。在她们怀孕前的几个月内，测试了包括皮质醇在内的应激激素水平。

在出生的婴儿中，有58个男孩和72个女孩。通常情况下，在英国，每出生100个女孩，就会有105个男孩诞生。
从佛罗里达州奥兰多市举行的会议上得知，比起压力最小的女性，压力最大的女性无法诞育男孩的可能性高达75%。当人们长期遭受压力时，比如工作压力和不良关系带来的压力，皮质醇水平就会上升。
我们尚且无法得知为什么高皮质醇水平会降低生育男孩的几率。
婴儿的性别是由男性精子的染色体决定的，这在受孕时已经确定。

但皮质醇水平过高，可能会使男性的胚胎在植入女性子宫时变得更加困难。

此外，男性婴儿可能更加脆弱，当皮质醇水平增高时，流产的可能性更大，这也导致了更多女婴的诞生。

• research [ri´sə:tʃ] n.&vi.调查；探究；研究 (初中英语单词)
• pressure [´preʃə] n.压榨 vt.对...施压力 (初中英语单词)
• instance [´instəns] n.例子，实例，例证 (初中英语单词)
• berlin [bə:´lin] n.柏林 (初中英语单词)
• stress [stres] n.强调；压力 vt.强调 (初中英语单词)
• conference [´kɔnfərəns] n.讨论(会)；会谈 (初中英语单词)
• florida [´flɔridə] n.佛罗里达 (初中英语单词)
• addition [ə´diʃən] n.加；加法；附加物 (初中英语单词)
• finding [´faindiŋ] n.发现物；判断；结果 (高中英语单词)
• oxford [´ɔksfəd] n.牛津 (高中英语单词)
• collapse [kə´læps] vi.&n.崩溃；病倒；衰败 (高中英语单词)
• phenomenon [fi´nɔminən] n.现象；奇迹；珍品 (高中英语单词)
• everyday [´evridei] a.每日的，日常的 (高中英语单词)
• trying [´traiiŋ] a.难堪的；费劲的 (英语四级单词)
• fragile [´frædʒail] a.易碎的；虚弱的 (英语四级单词)
• pregnant [´pregnənt] a.怀孕的；含蓄的 (英语六级单词)
• normally [´nɔ:məli] ad.正常情况下；通常 (英语六级单词)