Intra uterine fetal developmentIntra uterine fetal development

G&D of the fetus is typically divided into 3 G&D of the fetus is typically divided into 3 stages:stages:

1.1. Preembryonic (ovum) stage: fertilization to 2-Preembryonic (ovum) stage: fertilization to 2-3 weeks.3 weeks.

2.2. Embryonic stage : 4-8 weeks of gestation.Embryonic stage : 4-8 weeks of gestation.3.3. Fetal stage : 9 weeks after conception until Fetal stage : 9 weeks after conception until

birth.birth.

Preembryonic (ovum) stage: Preembryonic (ovum) stage: fertilization to 2-3 weeks.fertilization to 2-3 weeks.The conceptus: an ovum during the period from The conceptus: an ovum during the period from conception until primary villi appear 12-14 days after conception until primary villi appear 12-14 days after fertilization or 4 weeks since LMP.fertilization or 4 weeks since LMP.Rapid cell division and differentiation was occurred.Rapid cell division and differentiation was occurred.Develop embryonic membrane.Develop embryonic membrane.The inner cell mass of blastocyst forming fetus that the The inner cell mass of blastocyst forming fetus that the cells differentiate into three primary germs layers:cells differentiate into three primary germs layers:

A- the ectoderm (ecto =outside )A- the ectoderm (ecto =outside )Gives skin Gives skin ,,nails nails ,,tooth and nervous system.tooth and nervous system. B- The endoderm (endo = inner )B- The endoderm (endo = inner )Gives the epithelial inner lining of GITGives the epithelial inner lining of GIT, ,

respiratory system respiratory system , , endocrine glands and endocrine glands and auditory canal auditory canal

C- The mesoderm (meso = middle )C- The mesoderm (meso = middle )Gives the connective tissueGives the connective tissue ,muscle, blood and ,muscle, blood and

vascular system.vascular system.

Embryonic stage:4-8 weeks of gestationEmbryonic stage:4-8 weeks of gestation..Starts from the end of ovum stage until 8 weeks of Starts from the end of ovum stage until 8 weeks of gestation (or 10 weeks since LMP ) when the ovum gestation (or 10 weeks since LMP ) when the ovum measure approximately 3 cm.measure approximately 3 cm.The most critical stage of physical development as The most critical stage of physical development as highly vulnerable to teratogenes like: highly vulnerable to teratogenes like: virus virus ,,radiation radiation ,,infection and drugs. Developmental infection and drugs. Developmental interference during this stage lead to congenital interference during this stage lead to congenital anomalies.anomalies.

Organogenesis take place in this stage as the next:Organogenesis take place in this stage as the next: The first system to function is the cardiovascularThe first system to function is the cardiovascular,,the the

blood vessels begin early in the third weekblood vessels begin early in the third week,,heart start heart start to pump blood at 5to pump blood at 5thth week week ,,fetal heart rate is 120-160fetal heart rate is 120-160

Fetal circulation: the single umbilical vein carries Fetal circulation: the single umbilical vein carries oxygenated blood from the placenta.oxygenated blood from the placenta.

Two umbilical arteries return most of the mixed Two umbilical arteries return most of the mixed blood from fetus to placenta.blood from fetus to placenta.

The lung begins to grow as apart from upper The lung begins to grow as apart from upper digestive tract at the 4digestive tract at the 4thth week not functional week not functional until birth. A substance called surfactant form until birth. A substance called surfactant form in the lung at 27in the lung at 27thth week. week.

Alimentary tract (GI) formed at 4Alimentary tract (GI) formed at 4 thth week but week but function not accomplished before delivery.function not accomplished before delivery.

The kidneys develop rapidly as 5The kidneys develop rapidly as 5 thth week and week and begin to function and passing urine at 8begin to function and passing urine at 8 thth week. week.

The fetus is covered with a white The fetus is covered with a white ,,creamy creamy substance (skin)at 18th week and 20th week; substance (skin)at 18th week and 20th week; the fetus is covered by lanugo hair.the fetus is covered by lanugo hair.

CNS begins to develop at 3CNS begins to develop at 3rdrd week the neural week the neural tube complete at 4tube complete at 4thth week. week.

External genital are well enough developed External genital are well enough developed and can easily distinguished at 12 week.and can easily distinguished at 12 week.

At the end of 22 weeks the fetus is 210 mm length At the end of 22 weeks the fetus is 210 mm length and 630 gram weight . and 630 gram weight .

At the end of 26 weeks the fetus is 250 mm and At the end of 26 weeks the fetus is 250 mm and 1000 gram weight.1000 gram weight.

At the end of 30 weeks the fetus is 280 mm and At the end of 30 weeks the fetus is 280 mm and 1700 gram weight.1700 gram weight.

At the end of 34 weeks the fetus is 320 mm and At the end of 34 weeks the fetus is 320 mm and 2500 gram weight.2500 gram weight.

At the end of 38 weeks the fetus is 360 mm and At the end of 38 weeks the fetus is 360 mm and 3400 gram weight.3400 gram weight.

Fetal stage : 9 weeks after conception until Fetal stage : 9 weeks after conception until birthbirth

It starts from the embryonic stage until It starts from the embryonic stage until delivery of fetus .delivery of fetus .There is a change but not dramatic as in the There is a change but not dramatic as in the preceding stages.preceding stages.Every organ system and external structure is Every organ system and external structure is presented during this stage.presented during this stage.

The fetus can be detected by trans vaginal The fetus can be detected by trans vaginal ultrasound as early as 4 weeks after LMP and ultrasound as early as 4 weeks after LMP and by abdominal ultrasound in the second by abdominal ultrasound in the second trimester.trimester.

Fetal heart sound can be heard with fetoscope Fetal heart sound can be heard with fetoscope by 18-20 weeks of gestation and by electronic by 18-20 weeks of gestation and by electronic Doppler can detect heart motion at 10 week of Doppler can detect heart motion at 10 week of gestation.gestation.

Fetus is less vulnerable to teratogenes but me Fetus is less vulnerable to teratogenes but me interrupt normal functional development of interrupt normal functional development of organs particularly the brain. organs particularly the brain.