When Does Implantation Occur

When does implantation occur? This event, which signals the start of pregnancy, generally occurs 6 to 10 days after ovulation. This is generally days 20 to 24 of a menstrual cycle, if ovulation takes place on the 14th day. Days are counted from the first day of a period.

Fertilization and Implantation
Implantation is not the same thing as conception. Conception occurs when a sperm enters an egg and the egg begins to divide. The fertilized egg stays in the fallopian tube for three days. It then enters the uterus to begin implantation.

A fertilized egg must invade the endometrium in order to implant. Once this happens, it attaches to the wall of the uterus. Some women will notice the signs of implantation, while some do not feel anything. Some of the typical signs include

  • Spotting 7 to 10 days after ovulation
  • A rise in basal body temperature 7 to 10 days after ovulation has been confirmed
  • An implantation temperature dip that lasts for about a day, usually 7 to 10 days past ovulation

These symptoms do not always mean a woman is pregnant. A pregnancy test should be taken for more accurate results. If a fertilized egg fails to implant in the uterus, pregnancy will not occur, but a woman may show signs of chemical pregnancy on a pregnancy test. Implantation may fail because the uterine lining is not prepared for the embryo, or because the embryo has chromosomal abnormalities that prevent it from developing.

Implantation After IVF
In vitro fertilization (IVF) implantation follows the same approximate time frame. Implantation can start to take place 6 to 10 days after retrieval. The retrieval day is counted as Day 0. Five days after retrieval, the healthy embryo reaches the blastocyst stage, then in another one to two days, it will start to break out of the hard outer shell to begin the implantation process.

New research suggests that the location where the blastocyst is released can have an impact on successful implantation. In some cases, women may have more success with implantation if blastocysts are inserted directly into the uterus, rather than the fallopian tube.  

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