Gestation

妊rèn娠shēn, an ancient term^[1], commonly referred to as pregnancy.

Doctors typically consider the first day of a woman's last menstrual period as the start of pregnancy (the first week of gestation), calculating 40 weeks (or adding 280 days) as the due date; this period is known as the gestational period. Note that the start of gestation is not the date of fertilization, unless there is continuous monitoring with instruments, or there was only one instance of activity during ovulation, or it was achieved via in vitro fertilization; otherwise, it is difficult to accurately determine the date of fertilization.

The first 8 weeks after fertilization are referred to as the embryonic stage, while the later stage is known as the fetal stage.

Stages of Gestation

Although gestation is a continuous process, it is divided into three trimesters:

• First Trimester: 0 to 12 weeks
• Second Trimester: 13 to 24 weeks
• Third Trimester: 25 weeks until delivery

The following is a table of fetal development corresponding to gestational weeks 👉Source:

Gestational Weeks	Events
0	Early pregnancy The last stage before fertilization
2	Egg fertilization The fertilized egg begins to develop into a hollow sphere of cells (blastocyst)
3	The blastocyst implants into the uterine wall, and the amniotic sac begins to form
5	Areas that will form the brain and spinal cord (neural tube) begin to develop
6	The heart and major blood vessels begin to develop Heartbeat can be seen via ultrasound
7	Limbs begin to appear
9	Skeleton and muscles form Face and neck begin to develop Brain waves are detectable Skeleton formation; fingers and toes are visible.
10	Kidneys start functioning Almost all organs are fully formed Fetus begins to move and respond to touch (when stimulating the mother's abdomen) Mother gains weight, abdomen slightly bulges
14	Second trimester Fetal sex can be identified Fetus can hear
16	Fetal fingers can make a fist Fetal movements become stronger, so the mother can feel it Fat begins to be stored under the fetal skin, making the fetus appear fuller Hair begins to appear on the head and skin, with eyebrows and eyelashes emerging
20	Placenta is fully formed
24	Fetus can survive outside the womb Rapid weight gain for the mother
25	Third trimester Fetus is very active, frequently changing positions Lungs continue to develop Fetal head is down in preparation for delivery Fetus averages 50cm in length and weighs around 3kg Mother's abdomen enlarges, and the uterus protrudes
37-42	Delivery

Translation Note

The original language is Chinese, and the English translation was automatically generated by ChatGPT. There may be inaccuracies or errors in the phrasing, so please refer to the original text for accuracy.

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1. According to "Shuowen Jiezi": "妊 means pregnancy." 娠 refers to the fetus. Gestation first appeared in the Han Dynasty in Wang Chong's "Lunheng·Mingyi": "When pregnant, if one encounters evil, one suffers from thunder and rain changes, leading to early death." ↩︎