How long after pregnancy does the fetus enter the uterus?

This is an automatically translated article.

Article written by Dr. Nguyen Van Hung - Obstetrician and Gynecologist, Obstetrics Department - Vinmec Time City International Hospital

After the egg is fertilized, it takes about 10 to 12 hours for the fertilized egg to pass through the isthmus of the uterus. So after this process, how long is the slowest pregnancy in the uterus, is it a boy or a girl?

1. Time for the egg to move and implant in the uterus

After fertilization, the egg stays for about 48 hours in the balloon part of the fallopian tube. During this time, the fertilized egg performs mitotic activities, reaching the 2 to 8 cell stage (morula stage) and does not increase in volume. Elevated levels of progesterone from the ovarian corpus luteum relax the uterine muscles. The fertilized egg quickly crosses the isthmus of the uterus in about 10-12 hours. After this period, how long does it take for the fetus to enter the uterus at the latest? About 3 to 4 days after fertilization, the fertilized egg reaches the lining of the uterus and attaches to it at the 8-16 cell stage and the embryo continues to develop in the uterus until full term [ first].
However, during this time, pregnancy cannot be detected by fetal ultrasound, Beta hCG test can be detected in the mother's blood or urine about 6->14 days after fertilization.

2. "Is it a boy or a girl to get into the uterus late?"

Quite a lot of people wonder if "the late pregnancy is a boy or a girl". The time it takes for an embryo to reach the uterus is not related to the sex of the fetus. The transport of embryos in the fallopian tubes from the site of fertilization to the uterine cavity is influenced by [1]:
The activity of the villi in the fallopian tubes Activity of the uterine muscle layer: dependent on the concentration estrogen and progesterone The circulation of tubal fluid Details of the fetus's development week by week, every parent should learn:
The cases of embryos moving slowly into the uterus may be due to anatomical abnormalities of the fallopian tubes (usually due to factors such as infection, surgery, birth defects,...); anatomical abnormalities may be accompanied by functional impairment of the villi; abnormal levels of progesterone, estrogen; wrong date of fertilization,...

3. How to determine whether the pregnancy has entered the uterus or not?

Confirm the pregnancy has entered the uterus when the fetal ultrasound shows the gestational sac in the uterine cavity, however, the diagnostic criteria for the gestational sac are not clear. Terms such as "empty sac", "double decidua" or even "false gestational sac" cannot confirm or rule out an intrauterine pregnancy. Therefore, the diagnosis of intrauterine pregnancy is a subjective matter, depending on clinical and ultrasound features.
In the case of asymptomatic patients, it is recommended to wait until an embryo is found inside the gestational sac to confirm a true gestational sac [2].
Image of a normal gestational sac on ultrasound [3]:
A gestational sac can be seen on transvaginal ultrasound at 5 weeks' gestation Consists of two parts: the central non-echoic region (the extraembryonic body cavity) and the peripheral echoes (ring of trophoblasts). Surrounded by endometrium Eccentric position relative to the uterine axis The yolk sac: circular structure, visible on transvaginal ultrasound at 5.5 weeks gestation Before 6 weeks, embryos are very small in diameter < 4mm from 6-10 weeks embryo grows rapidly from 4-7mm at 6 weeks gestation to 31mm -32mm at 10 weeks gestation. Examine the fetal heart when fetal ultrasound shows the embryo and measure it with a vaginal probe at 6 weeks.

The first trimester is the most sensitive time during pregnancy. In order for mother and baby to be healthy, parents need to pay attention to:
Understand early signs of pregnancy, pregnancy poisoning, bleeding during pregnancy. Timely, correct and sufficient first prenatal check-up, avoiding too early/too late. Fetal malformation screening at 12 weeks detects dangerous fetal malformations that can be intervened early. Differentiate between normal vaginal bleeding and pathological vaginal bleeding for timely intervention to maintain pregnancy. Screening for thyroid disease in the first 3 months of pregnancy avoids dangerous risks before and during delivery. Vinmec currently has many maternity packages (12-27-36 weeks), in which the 12-week maternity package helps monitor the health of mother and baby right from the beginning of pregnancy, early detection and timely intervention of health issues. In addition to the usual services, the maternity monitoring program from 12 weeks has special services that other maternity packages do not have such as: Double Test or Triple Test to screen for fetal malformations; Quantitative angiogenesis factor test to diagnose preeclampsia; thyroid screening test; Rubella test; Testing for parasites transmitted from mother to child seriously affects the baby's brain and physical development after birth.
For detailed information about the 12-week maternity package and registration, you can contact the clinics and hospitals of Vinmec Health System nationwide.

Please dial HOTLINE for more information or register for an appointment HERE. Download MyVinmec app to make appointments faster and to manage your bookings easily.

References:
Textbook of Obstetrics and Gynecology (2016), Fertilization – nesting and egg development, Medical Publishing House, Hanoi. ISUOG (2013). ISUOG Practice Guidelines: performance of first-trimester fetal ultrasound scan: ISUOG Guidelines. Ultrasound Obstet Gynecol , 41 ( 1 ), 102–113. Carol B. Benson P.M.D. (2012), Alats of Ultrasound in Obstetrics and Gynocology , Wolters Kluwer, USA.