導讀:佩內洛普·切尼碰到朋友埃莉諾·馬歇爾時，她有個好消息要跟朋友分享：她懷孕了。埃莉諾也有個好消息，她也懷孕了......更讓人吃驚的是，兩人的預產期一樣，都是四月四號。那么兩人同一天生產的幾率到底有多大呢？

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?

佩內洛普·切尼碰到朋友埃莉諾·馬歇爾時，她有個好消息要跟朋友分享：她懷孕了。埃莉諾也有個好消息，她也懷孕了......更讓人吃驚的是，兩人的預產期一樣，都是四月四號。那么兩人同一天生產的幾率到底有多大呢？

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.

在英國，婦女預產期的推算，首先是根據最后一次生理期日期，加上280天，即40周。此后，進行超聲波掃描，根據胎兒的大小估算另一個預產期。若兩個“預產期”之間相差一周或者更久，則需進行更加準確的掃描。

It’s the same in most developed countries.

預產期的推算方法在大多數發達國家都相同。

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.

但是據一家非盈利組織圍產期研究所的數據表明，預產期很少準確。實際上，嬰兒在預產期誕生的幾率只有4%。

The figure is higher when premature births and pregnancies with complications are not included, but only marginally (4.4%).

若不考慮早產或者伴有并發癥的懷孕現象，那么該數據會高一些，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.

雖然預產期有助于父母了解孩子出生的時間，但是預產期最重要的是，為孕期中的媽媽“量身制定護理過程”，圍產期研究所的杰森·加多斯教授說道。

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.

他給孕婦的建議是，孩子可能在37周（259天）至42周（294天）期間的任何時候出生。這段時間成為“分娩期”，孩子在此期間已經發育完好。

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.

像佩內洛普和埃莉諾這樣的低危孕婦，60%的嬰兒將會與預產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，如上所說，只有4%的嬰兒會在預產期這天出生（若不考慮并發癥等，則有4.4%的嬰兒在預產期出生），也就是說幾率不到5%。

What, then, are the chances of Penelope’s and Eleanor’s babies both being born on 4 April?

那么佩內洛普和埃莉諾都在4月4號生產的幾率有多大呢？

Only 4.4% of 4.4%, or 0.2%.

只有4.4%的4.4%,或者說是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號之外的其他日子）的幾率更高，差不多為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".

加多斯稱，這些數據為孕婦揭示了一則重要信息。他說，“預產期”過于精確，容易引起誤導，應該將其稱為“估計日期”。

"Many mothers are unnecessarily anxious or impatient if there’s too much reliance on the expected date of delivery," Gardosi says.

“如果過于相信預產期，會讓很多媽媽感到焦躁。而這些焦慮根本沒有必要。”