Fetal development
Calculating the day your baby
starts growing and keeping track of pregnancy dates can be a daunting task. The
development of pregnancy is counted from the first day of the last normal
menstruation, although the development of the fetus begins only after
conception. Pregnancy is counted from this day because every time a woman has
her period, her body prepares for pregnancy.
The following information is
used as a general guide to healthy fetal development, although development may
vary depending on the health of the mother or miscalculation of ovulation.
Gestational age is the age of pregnancy from the last normal menstrual cycle,
while fetal age is the actual age of the growing baby.
Most pregnancy references
usually refer to gestational age rather than fetal developmental age, but we
have included both to clarify developmental stage. Measurements will be given
in total length from head to toe, but each pregnancy may vary in weight and
length and these are only general guidelines.
Pregnancy is also divided into
trimesters, each lasting 12 to 14 weeks. As with development, they can be
calculated from different dates, so not all quarterly calculations will be the
same. The following information divides the three quarters into just over 3
full months each.
The first trimester lasts from the 1st week to the end of the 13th week and includes 1, 2 and 3 months. The second trimester usually ends around the 26th week and consists of the 4th, 5th and 6th completed months. The third trimester can end anywhere between the 38th and 42nd week and corresponds to the 7th, 8th and 9th complete months of pregnancy.