Anecdotal evidence suggests labour can be induced by the lunar cycle and the start of a full moon.
If this is the case for the Duchess of Sussex, the full moon believed to be closest to Meghan’s expected due date is on Friday April 19.
Meghan has said her baby is due late April or early May, and by April 19 she is likely to be around or even beyond 37 weeks, when pregnancy is considered full-term.
April’s full moon is known as the Pink Moon, according to the Old Farmer’s Almanac.
The name comes not from its colour, but from the pink wildflowers that bloom in the early spring in the US and Canada.
In terms of labour, the suggestion is that a full moon’s gravitational pull affects the amniotic fluid in the same way it affects the water in the sea and rivers, as well as influencing the levels of the hormone melatonin.
Maternity wards are said to be busier during a full moon, although there is debate in the medical world about whether the moon does encourage women to go into labour.
When the Duchess of Cambridge gave birth to Prince George on July 22 2013, it was the day of a full moon.
She went into labour with Princess Charlotte two days before a full moon, but with Prince Louis the moon was only in its first quarter.
The Pink Moon is used to fix the date of Easter, which is always the Sunday after the first full moon following the Spring Equinox.
Easter Sunday this year is on April 21, also the Queen’s birthday, so Baby Sussex might even end up sharing a birthday with his or her great-grandmother.
There are also suggestions electrical storms and a drop in barometric pressure can bring on labour.
Just before Kate was admitted into hospital in 2013, western central London, near where her Kensington Palace apartment is based, experienced isolated heavy rain, thunder and lightning strikes.