The duration of a pregnancy is divided into 3 trimesters, each of which is a little longer than 13 weeks. The 1st month marks the beginning of the first trimester of pregnancy.
Gestational age
The time of pregnancy is measured according to the “gestational age” which begins on the first day of the last menstrual period (PML). Gestational age is often confusing.
- Most people think that a pregnancy lasts 9 months.
- However, since it is measured from the first day of (your) last menstrual period, so about 3-4 weeks before you actually got pregnant, full-term pregnancy will usually happen about 40 weeks from the first day of the last menstrual period (PML) – about 10 months.
However, since many women do not remember exactly when they “started” their last menstrual cycle, the surest way to know gestational age is an ultrasound at the beginning of pregnancy.
The first two weeks
The first two weeks of pregnancy are the first 2 weeks of your menstrual cycle.
- You have your period.
- About 2 weeks later, the most mature egg is released from the ovary: this is ovulation.
- Ovulation can occur earlier or later, depending on the length of the menstrual cycle.
- An average menstrual cycle is 28 days.
After it is released, your egg travels down the fallopian tube to the uterus.
- If the egg meets a sperm, they combine.
- This “combination” is called fertilization.
- Fertilization is more likely to occur when you have unprotected sex during the 6 days prior to ovulation.
The 3rd and 4th week
During the 3rd and 4th week of pregnancy, the fertilized egg descends down the fallopian tube and divides into more and more cells.
- About 3-4 days after fertilization reaches your uterus.
- Then the dividing cells form a ball that floats in the uterus for about 2 – 3 days.
- Pregnancy begins when the sphere of fertilized cells attaches to the lining of the uterus.
- This operation is called implantation.
- It usually begins about 6 days after fertilization and takes about 3-4 days to complete.
- Up to half of the fertilized eggs leave your body when you get your period before the implant is complete.
Even when an egg is fertilized by sperm, it is not said that there is always a pregnancy.
The very first symptoms of pregnancy
For many women the first sign of an ongoing pregnancy is a missed period. When the period is missed, most pregnancy tests will come back positive.
Other symptoms present at the beginning of pregnancy may be: a feeling of tiredness, a feeling of bloating, a pee greater than usual, mood swings, nausea and tender or swollen breasts.
Not all women have all of these symptoms, but it’s a common thing to have at least one.
Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.
She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform, Maternicity.com.