What is the Two-Week Wait?
The two-week wait (TWW) refers to the time between ovulation and a period, also known as the luteal phase of the menstrual cycle. In this time frame, a sperm can fertilize an egg and the resulting embryo can implant into the uterine lining (endometrium) to initiate a pregnancy. If fertilization and implantation occur and the pregnancy continues, the woman will not have a menstrual cycle throughout the duration of her pregnancy. If these events do not occur, the endometrium will shed, the woman will get her period, and her menstrual cycle will begin again. Near the end of the TWW, a woman can take a urine or blood pregnancy test to determine if she is pregnant.
The TWW and IVF
The TWW also refers to the time frame between an embryo transfer (following IVF) and a clinical (blood) pregnancy test, though this time frame is usually not two weeks long. In the days following an embryo transfer, the embryo, which was created in a lab via IVF, moves around the uterus until it finds a spot on the endometrium to implant. A clinical pregnancy test is normally scheduled 9-11 days after an embryo transfer depending on your clinic’s protocol. If you are taking medications such as progesterone, it’s important to continue taking these medications until your doctor instructs you to stop.
hCG Results
When an embryo implants into the endometrium, some of its cells begin to develop into the placenta. These cells produce the hormone human chorionic gonadotropin (hCG) in increasing amounts. Home pregnancy tests will reveal a positive result once the urine hCG levels reach a certain amount. Clinical pregnancy tests measure hCG levels in the blood (often called a beta hCG test). Though some medications (such as an hCG trigger prior to your transfer) can skew hCG results, an initial result of 5 mIU/mL is considered positive (though a result of ≥25mIU/mL is considered a “safe” result (source: Everything About HCG Levels in Pregnancy | What Is hCG? (americanpregnancy.org)). It’s most important that hCG levels continue to rise appropriately, doubling roughly every 72 hours.
Following hCG results
Depending on your hCG results, your clinic may perform an ultrasound examination in your sixth week of pregnancy (roughly 4 weeks after your embryo transfer). These typically follow positive or questionable hCG results to determine:
where an embryo implanted (this normally occurs in the uterus but, at times, can occur outside of the uterus and result in an ectopic pregnancy)
The size of the gestational sac (AKA amniotic cavity) and presence of a fetal pole. You may also be able to see the yolk sac. These markers determine how the pregnancy is progressing.
if possible, what the fetal heart rate is (though it’s often too early to detect this at 6 weeks)
Follow up ultrasounds are normally performed before you are released to an OBGYN. Please note that these policies and procedures may differ between clinics, and it’s possible to have varying results at these appointments.
A Biochemical Pregnancy
If hCG levels are initially positive but decline, it’s possible that you are experiencing a biochemical pregnancy. This means that implantation occurred but the embryo did not continue developing properly, though the pregnancy was never confirmed via ultrasound examination.
