Fetal Development Weeks 1 Through 4

See what's happening with your baby in the first month of your pregnancy.

By the editors of Parents magazine

Prev 1 2 3 (of 4) Next

Week 1

Because the date of ovulation is often difficult to pinpoint, medical experts usually use the first day of your last period as the official beginning of the 40 weeks of pregnancy, and as the starting point in calculating your baby's gestational age.

Therefore, the extraordinary process by which your baby comes to life actually begins with an utterly ordinary event--your monthly period. During your last period before conception, the groundwork for pregnancy is already being laid. The previous month's uterine lining, called the endometrium, is shed, along with some blood, resulting in menstrual flow. Meanwhile, follicle stimulating hormone (FSH) kicks into gear, triggering the development of several ovarian follicles. Located deep in the ovary, these yellow bulbs each contain a single immature egg. As the bulbs grow, the eggs begin to mature. The follicles also signal the ovary to produce estrogen, a key hormone in bringing about ovulation.

Next: Week 2

Related Links

Topics in Pregnancy Stages

Second Trimester Tests

Comments Comments ( 6 )

lilbrowneyedgrl89 wrote:

ive taken a pregnancy test a couple of weeks ago and it came out negative but this past week i was supposed to start my period but it still hasnt come but ive been having the worst cramps. they're even worse than usual. they hurt so much im awoken out of my sleep at night. what could be causing this?

11/14/2009 05:44:45 AM Report Abuse

tracie3521921 wrote:

lotumala how old are you

11/10/2009 08:27:19 PM Report Abuse

lotumala wrote:

i am confused, i usually have my periods every 20 -24 days of the month i may have two periods twice a month and before my period comes my breast is alway very painful and full.also my tube was tied 13yrs ago after i had my second baby.my last period was oct 3rd. and have not seen my period as of today.i used the home pregnance test it was negative. my breast is not tender but a little full. what advice can you give me

11/8/2009 03:50:29 PM Report Abuse

jackig3 wrote:

im trying to figure out if im pregnant. this is only our first month trying, my period is late which is normal for me but i have 7 out of the 13 signs that are on here. and cramping is not normal for me between periods but the pregnancy tests are all coming back negaitive.

11/3/2009 06:39:35 PM Report Abuse

us3post wrote:

Take a pregnancy test. That is the best way to know.

11/1/2009 10:35:48 AM Report Abuse

Add your comment

You must be logged in to leave a comment. Register | Log In