导读:佩内洛普·切尼碰到朋友埃莉诺·马歇尔时，她有个好消息要跟朋友分享：她怀孕了。埃莉诺也有个好消息，她也怀孕了......更让人吃惊的是，两人的预产期一样，都是四月四号。那么两人同一天生产的几率到底有多大呢？
When Penelope Chaney met up with her friend, Eleanor Marshall, she had good news to share - she was pregnant. But Eleanor also had good news... she was pregnant too. And amazingly, both had been given the same predicted delivery date - 4 April. So what are the chances of both giving birth on the same day?
佩内洛普·切尼碰到朋友埃莉诺·马歇尔时，她有个好消息要跟朋友分享：她怀孕了。埃莉诺也有个好消息，她也怀孕了......更让人吃惊的是，两人的预产期一样，都是四月四号。那么两人同一天生产的几率到底有多大呢？
In the UK，a woman’s estimated date of delivery is first calculated by using the date of her last period and adding 280 days, or 40 weeks. That is followed by an ultrasound scan where another estimate is made, based on the size of the foetus. If the two "due dates" differ by a week or more, the scan is taken as the more accurate measure.
在英国，妇女预产期的推算，首先是根据最后一次生理期日期，加上280天，即40周。此后，进行超声波扫描，根据胎儿的大小估算另一个预产期。若两个“预产期”之间相差一周或者更久，则需进行更加准确的扫描。
It’s the same in most developed countries.
预产期的推算方法在大多数发达国家都相同。
But data from the Perinatal Institute, a non-profit organisation, shows that an estimated date of delivery is rarely accurate - in fact, a baby is born on its predicted due date just 4% of the time.
但是据一家非盈利组织围产期研究所的数据表明，预产期很少准确。实际上，婴儿在预产期诞生的几率只有4%。
The figure is higher when premature births and pregnancies with complications are not included, but only marginally (4.4%).
若不考虑早产或者伴有并发症的怀孕现象，那么该数据会高一些，但也只是稍微高一些（4.4%）。
While it may be helpful for parents to get an idea of when their child will arrive, the main purpose of the due date is to "define a metric for the care" of the mother during pregnancy, says Prof Jason Gardosi of the Perinatal Institute.
虽然预产期有助于父母了解孩子出生的时间，但是预产期最重要的是，为孕期中的妈妈“量身制定护理过程”，围产期研究所的杰森·加多斯教授说道。
The advice to the expectant mother, he says, that the baby is likely to come any time between 37 weeks (259 days) and 42 weeks (294 days), a period referred to as "term", when the baby has reached full maturity.
他给孕妇的建议是，孩子可能在37周（259天）至42周（294天）期间的任何时候出生。这段时间成为“分娩期”，孩子在此期间已经发育完好。
For women like Penelope and Eleanor, whose pregnancies are low risk, 60% of babies are born within a week either side of the estimated date of delivery.
像佩内洛普和埃莉诺这样的低危孕妇，60%的婴儿将会与预产期前一周或后一周出生。
But, as noted above, only 4% (or 4.4%, ignoring pregnancies with complications etc) are born on the predicted date itself - in other words, the chance of this happening is less than one in 20.
但是，如上所说，只有4%的婴儿会在预产期这天出生（若不考虑并发症等，则有4.4%的婴儿在预产期出生），也就是说几率不到5%。
What, then, are the chances of Penelope’s and Eleanor’s babies both being born on 4 April?
那么佩内洛普和埃莉诺都在4月4号生产的几率有多大呢？
Only 4.4% of 4.4%, or 0.2%.
只有4.4%的4.4%,或者说是0.2%.
The chance that their children will be born on the same day - any day, not necessarily 4 April - is higher. It’s about one in 30.
但是孩子在同一天出生（除4月4号之外的其他日子）的几率更高，差不多为1/30.
Gardosi says the statistics reveal an important message for pregnant women. The phrase "due date" is misleading, that makes it sound too accurate, he says - it should really be called an "estimated date".
加多斯称，这些数据为孕妇揭示了一则重要信息。他说，“预产期”过于精确，容易引起误导，应该将其称为“估计日期”。
"Many mothers are unnecessarily anxious or impatient if there’s too much reliance on the expected date of delivery," Gardosi says.
“如果过于相信预产期，会让很多妈妈感到焦躁。而这些焦虑根本没有必要。”
