As the pregnancy grows it releases the pregnancy hormone called human chorionic gonadotropin (hCG) into the maternal blood. This hormone can be detected one week after implantation (28 days from the beginning of the menstrual period and 2 weeks after ovulation) in the blood or urine. So, pregnancy officially begins at the time of implantation but is usually not detectable until the pregnancy hormone shows up in the blood and urine.
https://www.sharecare.com/health/fertility-pregnancy-childbirth/when-does-pregnancy-begin
Takeaway. 1  The first trimester of pregnancy starts without any signs that you’re pregnant. 2  It ends with a body that’s adjusted to carrying a child. 3  Noticeable symptoms won’t start until the fourth week.  Morning sickness may begin around week five or six, but nausea and vomiting can happen any time of the day.
http://www.healthline.com/health/pregnancy/early-symptoms-timeline
Takeaway. 1  The first trimester of pregnancy starts without any signs that you’re pregnant. 2  It ends with a body that’s adjusted to carrying a child. 3  Noticeable symptoms won’t start until the fourth week. This is when a woman can expect to miss her period and may experience mild cramping and blood spotting.
http://www.healthline.com/health/pregnancy/early-symptoms-timeline
Approximately 1 week later, 7-8 days after ovulation and 21-22 days after the beginning of the menstrual period, the embryo (fertilized egg) implants into the inner lining of the uterus called the endometrium and quickly sets up a connection with maternal blood vessels.
https://www.sharecare.com/health/fertility-pregnancy-childbirth/when-does-pregnancy-begin
The process of prenatal development occurs in three main stages. The first two weeks after conception are known as the germinal stage; the third through the eighth week are known as the embryonic period, and the time from the ninth week until birth is known as the fetal period.
https://www.verywell.com/stages-of-prenatal-development-2795073
Every woman’s cycle is different but here is how your cycle approximately goes. It begins on the first day of your period. Approximately 2 weeks after your period begins, you ovulate (an egg is released from your ovary into your fallopian tube) and this is the time you are most likely to get pregnant.
http://www.urbanmommies.com/pregnancy-begins-signs-of-implantation/
You will likely miss your next period four weeks after conception. If you have an irregular period, you’ll want to take a pregnancy test to confirm. Most home tests can detect hCG as soon as eight days after a missed period. A pregnancy test will be able to detect hCG levels in your urine and show if you are pregnant.
http://www.healthline.com/health/pregnancy/early-symptoms-timeline
The mass of cells is now known as and embryo. The beginning of the third week after conception marks the start of the embryonic period, a time when the mass of cells becomes distinct as a human. The embryo begins to divide into three layers each of which will become an important body system. Approximately 22 days after conception, the neural tube forms.
https://www.verywell.com/stages-of-prenatal-development-2795073
Pregnancy and Conception. Most of the time, you won't know the exact day you got pregnant. Your doctor will count the start of your pregnancy from the first day of your last menstrual period. That's about 2 weeks ahead of when conception happens. Here's a primer on conception: Ovulation. Each month inside your ovaries, a group of eggs starts to grow in small, fluid-filled sacs called follicles.
http://www.webmd.com/baby/understanding-conception
Some scientists say that implantation is when and where pregnancy begins. What is implantation and are there any common signs of implantation? Implantation occurs when the egg that has been fertilized by the sperm attaches to the inner wall of the uterus about 7-9 days after conception. Having traveled down the fallopian tube and divided several times, the fertilized zygote has reached its final destination in the warm and nourishing uterine lining.
http://www.urbanmommies.com/pregnancy-begins-signs-of-implantation/
which period begins three weeks after conception
The embryonic period begins three weeks after conception. Embryonic period begins three weeks after conception.