Pregnancy is the physical state when a women carries an embryo or fetus inside her uterus. Pregnancy includes the period from conception to birth. Pregnancy lasts about 40 weeks, which is measured from the first day of the woman's last menstrual period to childbirth. Starting the count from the date of a woman's last period is common worldwide and is done so for consistency.
Physicians measure a pregnancy term in weeks. This is because months vary in length while weeks are always seven days long.
Days in a Pregnancy
There are about 280 days in a pregnancy (40 weeks x 7 days per week). This number is an average for all women; some pregnancies are longer and some are shorter.
Months in a Pregnancy
A pregnancy is often considered to be nine months. This can be confusing because 40 weeks easily leads to 10 months; however, months are not exactly four weeks long.
Pregnancy is divided into three trimesters. Each trimester is about 12 weeks. Trimesters are used for medical reasons, including risk identification and fetus development.
The actual length of a pregnancy will vary due to several factors, including actual conception date, maternal health, previous pregnancy history and genetics.