Fetal Development

The earliest an ultrasound can possibly determine the gender of a fetus is 12 weeks. Most doctors won't attempt to determine the gender until 16-20 weeks. Unlike amniocentesis, ultrasound genderizing isn't an exact science. Depending on the way the baby lays, it can be difficult to see the genitals. Some radiologists will influence the baby to move into a different position to catch a glimpse, or you could consume something containing sugar to make the fetus more active. Amniocentesis, if you have to have one done, determines the gender through chromosomal analysis and this is fool-proof.

Other answers from contributors:

• You can probably see the sex of the fetus by three months. By then organs are already developed.

• It seems the common answer on the Internet is 16-18 weeks.

• Sometimes you can tell early and sometimes you can't tell until they are born. I found out that my child was a boy at 17 weeks, but my friend didn't find out until when she had hers, and it was a girl. They had taken many ultrasounds but the baby was so lady-like she just didn't want anyone to see!

• I would agree with the last person's answer. It all depends on how modest your baby is, and how he or she likes to lay. If those legs are closed, you may be waiting until delivery! If you have a good radiologist, they may be able to coax the baby into a slightly different position. At my office (I work at an OB/GYN office), we sometimes tell moms to drink a Hi-C juice box (nothing w/ caffeine, just a little dose of sugar) to get the baby nice and active. Check with your doctor on this first, though.

• As the sexual organs are not differentiated until 16-17 weeks (before this boys and girls look the same) this is the earliest an ultrasound can tell you. Chorionic villus sampling and amniocentesis will tell you before this.

• I knew I was having a boy at 14 weeks. It's all dependent on how your baby is positioned. My sister wasn't able to tell what her first kid was because she (the fetus) had her legs crossed during the ultrasound.

• It's also a lot easier (for obvious reasons) to tell if it's a boy than if it's a girl.

• I found out that I was having a girl at 20 weeks! But it just depends on how the baby cooperates with the ultrasound tech.

24 hours after fertilization:the single celled egg has split into two identical sister cells

32 hours after fertilization:the two identical sister cells have divided into four cells

36 hours after fertilization: the egg has divided into eight cells

4 days after fertilization: embryo enters the uterus at the morula stage of development

6-7 days after fertilization:the egg enters the blastula stage

7-8 days after fertilization:the blastula hatches from the pelucida

2 weeks after fertilization: the blastocyst elongates and comes in contact with the uthrine wall

14-16 days after fertilization: binucleate cells begin to differnentiate in the trophoblast

16 days afer fertilization:

20 days after fertilization: the embryo's heart begins to beat

30 days after fertiliziation: the embryo is about a ½ inch long

31-42 days after fertilization:major growth is taking place

42 days after the fertilization:the embryonic period is at an end and it is about 1½ inches long

60 days after fertilization: the fetus is about 4 inches long and eyes, eyelids, and nostrils can be identified

3 months after fertilization:the fetus is about 10 inches long and fine hair is visible on the head

145-150 days after fertilization:the lambs are born

The first two weeks of a pregnancy, actually happens before conception, as your body, first sheds the uterine lining from the previous cycle - starting with day one of menstruation. Once menstruation stops the lining begins to replace itself and several follicles on each ovary begin to mature.

In the first days after menstruation ends, the cervical mucus stays thick to prevent any bacteria from entering the uterus. As your body prepares to ovulate, the cervical mucus becomes thin and slippery, your cervix drops forward and the Os opens slightly to allow sperm to enter the uterus. The fluid in the semen and cervix will now preserve and nourish any sperm healthy enough to go the distance - as they wait for up to five days for the first ovum to become ripe and the ovarian follicle to rupture with a single ova ready to join with the first sperm cell that breaks through the cell's surface. You are now about half way through your monthly cycle.

Once ovulation occurs and a single sperm out of the millions in a normal ejaculation breaks through the membrane of the mature ova - they become one - instantly developing a protective barrier so no other sperm can enter the fertilized ovum. The Os closes, the cervix backs up, fresh cervical mucus develops into a mucus plug that sits tight in the Os until the woman is ready to deliver - this prevents anything foreign from entering the uterus - as progesterone tells the uterus not to break down it's fresh, new lining.

Chemical and hormonal activity do an amazing synchronized dance - as these two cells merge fully encoded with all the information that goes into making a baby; the gender, eye & hair color, body build and height, even the baby's IQ, and all the organs this baby will need to be fully functioning, prior to birth - are in place and waiting their turn to make this into a human being from the moment of conception. In these first days the two cells are dividing rapidly, separating and getting into order. Our amazing hormones protect this tiny group of cells, days before our conscious self has any awareness of the new life growing within.

As the cells continue to divide, they are now formed into a blastocyst that works it's way from the fallopian tube to the uterus, as it does a free-fall into the uterine cavity it will grab onto the lining of the uterine wall. Just days after conception this gives some women their first inkling they may be pregnant, as their baby-to-be implants itself - the woman may experience cramping or light spotting shortly before the time their period should be due. Following this, most woman start developing early symptoms of pregnancy - breast tenderness, fatigue, nausea and hormonal shifts that turn their moods 180 degrees in the blink of an eye. All caused by the defining hormone of pregnancy hCG(human chorionic gonadotropin)

Prior to implanting into the uterus, about 6 days after conception - the mass of cells had developed into 3 distinct layers. One that becomes the placenta, which will nourish and protect this new person for the remainder of the pregnancy - the umbilical cord, which is the lifeline between mother and baby - and the baby itself - All this happens before most women even know they have conceived!

Once the early placenta starts growing, hCG is being produced and rising quickly, from it's normal level of 0 to 5 - it will double every 72 hours and in just a few days it reaches 25mIU/ml - a serum level that is the standard laboratory proof of a an early pregnancy - two or three days later the level will reach a strong enough urine concentration to trigger a positive result in the HPT / EPT. Usually between 50mIU/ml and 100mIU/ml depending on the sensitivity of the brand of testing device. The hormone will continue to rise for 11 weeks, as it protects and cares for your growing baby - until the placenta is fully functioning and takes over at 12 weeks - the start of the second trimester.

Two weeks after conception your baby to be is just .078" - although not yet visible there is already movement in the developing main blood vessels and arm and leg buds have started to grow. A little tiny miracle in the making.