Embryo growth, signs of fetal maturity

Germ growth

A. 21-day-old human embryo B. 4-week-old embryo. C. beginning of limb formation D. 2 month old embryo

In the embryonic period, before the shape of the embryo begins to form, we measure the largest length of the germinal target. For embryos where the limbs are just beginning to form, we measure the length of the embryo from the vertex to the coccyx = tectococcal length (TCD) - the so-called sitting length. In the embryonic period, we can estimate age by the number of somites. For fetuses with developed lower limbs, we measure the length from crown to heel = crown-to-back length - the so-called standing length.

Changes in body proportions

Especially in the embryonic period, the development of individual parts of the body is not proportional. From the beginning, the head part of the embryo and the body grow. Towards the end of the embryonic period, the head is about ½ the length of the entire body and the limbs are relatively short. During the fetal period, the limbs and trunk size increase more compared to the head size. In a newborn baby, the head makes up about ¼ of the total length. Postnatally, this development continues, as the adult head corresponds to 1/8 of the entire body.

Estimation of the age of the embryo

An acceptable estimate of the age of the embryo is based on:

• the first day of the last menstural period;
• estimation of the moment of fertilization (conception);
• fertilization sonographic measurement of the chorionic sac and the embryo;
• examination of the external features of the embryo.

Growth in length is significant during the 3rd to 5th month. Significant weight gain occurs during the 8th and 9th months.

Signs of fetal maturity

• Length 50 cm;
• weight over 3000 g;
• well-formed subcutaneous fat (body contours are rounded);
• the skin is pink, bald, only on the shoulders and back there are remnants of lanuga;
• eyebrows and eyelashes are well formed;
• the hair is several centimeters long;
• nails extend beyond the ends of the fingers;
• the bones of the skull are hard, the small and large fontanelles are palpable and separate from each other;
• in boys the testicles descend into the scrotum, in girls the labia minora are completely hidden between the labia majora;
• the newborn cries loudly and moves.

Birth

The normal duration of pregnancy lasts approximately 280 ± 14 days, which is determined by the last menstrual period (from the 1st day of the last period). This is the so-called menstrual age. Pregnancy lasts 10 lunar months (28 days). The expected date of childbirth is approximately 266 days from conception, the so-called fertilization/conception age.

The due date is calculated: 1st day of the last period - 3 months + 1 year + 1 week. Iron

Stages of childbirth

• First (opening) time:
  • dilatation of the birth canal, rupture of the amniotic sac, outflow of amniotic fluid. Maximum dilatation of the uterine cervix ("the disappearance of the cervix"), the enlarged lower uterine segment merges with the vagina into a single birth canal. The main role is played by uterine contractions. Time: 8-12 hours.
• Second (expulsion) period:
  • passage of the fetus through the birth canal (30-60 minutes for primiparous, less for multiparous), the fetus is expelled by uterine contractions and with the participation of the abdominal press.
• Third period (bed time):
  • expulsion of the placenta with amniotic sacs (15–30 minutes). It begins with the separation of the placenta from the uterine wall by uterine muscle contractions (sudden shortening of muscle bundles to prevent bleeding) followed by uterine contractions that complete the process. When the placenta descends into the vagina, it causes the reflex pressure of the abdominal press, which pushes the placenta with its envelopes outward.

Links

Related articles

• Birth
• First segment

Sources

• JIRSOVÁ, Zuzana. Growth of the embryo, determination of the age of the embryo. Childbirth, signs of fetal maturity [lecture for subject Department of General Medicine, specialization General Histology and General Embryology, 1. faculty of medicine Charles University]. Praha. 2014-01-02. 

• MALÍNSKÝ, Jiří – LICHNOVSKÝ, Václav. Přehled embryologie člověka v obrazech. 4. edition. Olomouc : Univerzita Palackého v Olomouci, 2008. ISBN 978-80-244-2251-0.

Recommended literature

• SADLER, Thomas W – SINHA, M.D. Langmanova lékařská embryologie. 1st Czech edition edition. Praha : Grada, Grada. pp. 414. ISBN 978-80-247-2640-3.