FETAL Growth & Development US

1ST trimester PG
Soft Markers are features that may indicate aneuploidies in a fetus  
NORMAL LT vs  DOWN SYNDROME RT
  normal nuchal thickness in (LT image) 1st trimester is ~ less than 3 mm /1 
BUT increased nuchal thickness (RT image) = is a soft marker for Down syndrome
2/    there is a normal nasal bone (echogenic) (LT image) But absent nasal bone (RT image) which is a soft marker indicating Down syndrome
3/  ecogenic intracardiac focus is a hyperechoic structure seen within the fetal heart (RT image), looks like a hyperechoic dot indicating Down syndrome But No such dot in the normal (LT image)
4/ normal lateral ventricles measurement (LT image) usually less than 10 mm BUT in the (RT image) there is mild ventriculomegaly (dilatation of lateral ventricle) measuring more than 10 mm which is a soft marker for Down syndrome
5/ normal nuchal thickness in 2nd trimester (LT image) must be less than 6 mm, it can be measured in the transverse view of the fetal brain at the level of the cerebellum BUT there is increased thickness in the (RT image) indicating Down syndrome
6/   in coronal view of the fetal abdomen (LT image) there is no any hyperechoic region BUT associated wit Down syndromein the (RT image) there is hyperechogenic bowl which is seen in fetus with Down syndrome
 7/  a short femur for gestational age (RT image) is seen in many congenital anomalies.. it can be seen in Down syndrome
   8/  a short humerus is also associated with Down syndrome
 9/ ..dilated fetal renal pelvis (RT image) is also associated with Down syndrome
the AP diameter of the renal pelvis is more than 4 mm till 28 wks & more than 7 mm after 28 wks
 The normal measurement of the renal pelvis is 0-7mm before 24 weeks and less than 10mm after 28weeks. If the measurement is more than this, it is called renal pelvis dilatation
10/ abnormal spectral doppler waveform of the Ductus Venosus is also associated with Down syndrome  
 (normally it has a triphasic pattern)
 11/    a venricular septal defect (VSD) seen in (RT image), a discontinuity in the interventricular septum, is a soft marker for Down syndrome
in a transverse view of the fetal abdomen, a normal fetal stomach is seen as a round ANECHOIC structure but, 
in the same view a birth defect known as ESOPHAGEAL atresia, is seen, indicating a soft marker for DOWN syndrome
IN this anomaly the esophagus does not develop properly leading to non visualization of the stomach because NO fluid reaches the stomach & te stomach remais persistently invisible     
 12/    duodenal atresia can lead to a dilated stomach & duodenum giving a double bubble appearance which in some cases is associated with Down syndrome
ultimately, Down syndrome is diagnosed with invasive tests such as chorionc villous sampling & amniocentesis

1ST trimester PG
Soft Markers are features that may indicate aneuploidies in a fetus  
NORMAL LT vs  DOWN SYNDROME RT
  normal nuchal thickness in (LT image) 1st trimester is ~ less than 3 mm /1 
BUT increased nuchal thickness (RT image) = is a soft marker for Down syndrome
2/    there is a normal nasal bone (echogenic) (LT image) But absent nasal bone (RT image) which is a soft marker indicating Down syndrome
3/  ecogenic intracardiac focus is a hyperechoic structure seen within the fetal heart (RT image), looks like a hyperechoic dot indicating Down syndrome But No such dot in the normal (LT image)
4/ normal lateral ventricles measurement (LT image) usually less than 10 mm BUT in the (RT image) there is mild ventriculomegaly (dilatation of lateral ventricle) measuring more than 10 mm which is a soft marker for Down syndrome
5/ normal nuchal thickness in 2nd trimester (LT image) must be less than 6 mm, it can be measured in the transverse view of the fetal brain at the level of the cerebellum BUT there is increased thickness in the (RT image) indicating Down syndrome
6/   in coronal view of the fetal abdomen (LT image) there is no any hyperechoic region BUT associated wit Down syndromein the (RT image) there is hyperechogenic bowl which is seen in fetus with Down syndrome
 7/  a short femur for gestational age (RT image) is seen in many congenital anomalies.. it can be seen in Down syndrome
   8/  a short humerus is also associated with Down syndrome
 9/ ..dilated fetal renal pelvis (RT image) is also associated with Down syndrome
the AP diameter of the renal pelvis is more than 4 mm till 28 wks & more than 7 mm after 28 wks
 The normal measurement of the renal pelvis is 0-7mm before 24 weeks and less than 10mm after 28weeks. If the measurement is more than this, it is called renal pelvis dilatation
10/ abnormal spectral doppler waveform of the Ductus Venosus is also associated with Down syndrome  
 (normally it has a triphasic pattern)
 11/    a venricular septal defect (VSD) seen in (RT image), a discontinuity in the interventricular septum, is a soft marker for Down syndrome
in a transverse view of the fetal abdomen, a normal fetal stomach is seen as a round ANECHOIC structure but, 
in the same view a birth defect known as ESOPHAGEAL atresia, is seen, indicating a soft marker for DOWN syndrome
IN this anomaly the esophagus does not develop properly leading to non visualization of the stomach because NO fluid reaches the stomach & te stomach remais persistently invisible     
 12/    duodenal atresia can lead to a dilated stomach & duodenum giving a double bubble appearance which in some cases is associated with Down syndrome
ultimately, Down syndrome is diagnosed with invasive tests such as chorionc villous sampling & amniocentesis

Fetal Growth and Development

Karin M. Fuchs MD, in Fetal and Neonatal Secrets (Third Edition), 2014


When in gestation do the five senses develop in the fetus?

Touch: Between 8 and 15 weeks of gestation, the fetal somatosensory system develops in a cephalocaudal pattern. By 32 weeks of gestation, the fetus consistently responds to temperature, pressure, and pain.

Taste: Taste buds are morphologically mature by 13 weeks of gestation. By 24 weeks of gestation, gustatory (taste) responses may be present.

Hearing: Auditory function begins at 20 weeks of gestation, when the cochlea becomes functional. By 25 weeks of gestation, response to intense vibroacoustic stimuli can be elicited. Sensitivity and frequency resolution approach adult level by 30 weeks of gestation and are indistinguishable from the adult by term.

Sight: Pupillary response to light appears as early as 29 weeks of gestation and is present consistently by 32 weeks of gestation.

Smell: By 28 to 32 weeks of gestation, premature infants appear to respond to concentrated odor ^∗†

Fetal Water Compartments

In gestation, water is partitioned between the 1/ fetus, 2/ placenta and 3/ membranes, and 4/ AF. Although term human fetuses may vary considerably in size, an average fetus contains 3000 mL of water, of which about 350 mL is in the vascular compartment. In addition, the placenta contains another 500 mL of water. More precisely, the volume of fetal and placental water is proportionate to the fetal weight. AF volume is less correlated with fetal weight. The AF is a fetal water depot,¹⁰ and in normal human gestations at term, the AF volume may vary from 500 mL to more than 1200 mL.¹¹ In pathologic states, the AF volume may vary more widely. Below we present what is known regarding the formation of AF, the circulation of AF water, and the mechanisms controlling this circulation.
^{https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/pregnancy}

During pregnancy, the fetal circulatory system works differently than after birth:

• The fetus is connected by the umbilical cord to the placenta. This is the organ that develops and implants in the mother's uterus during pregnancy.
  
• Through the blood vessels in the umbilical cord, the fetus gets all needed nutrition and oxygen. The fetus gets life support from the mother through the placenta.
  
• Waste products and carbon dioxide from the fetus are sent back through the umbilical cord and placenta to the mother's circulation to be removed.
  
• The fetal circulatory system uses 3 shunts. These are small passages that direct blood that needs to be oxygenated. The purpose of these shunts is to bypass the lungs and liver. That's because these organs will not work fully until after birth. 1/ The shunt that bypasses the lungs is called the foramen ovale. This shunt moves blood from the right atrium of the heart to the left atrium. 
  
• The 2/ ductus arteriosus moves blood from the pulmonary artery to the aorta.
  Oxygen and nutrients from the mother's blood are sent across the placenta to the fetus. 
  
• The enriched blood flows through the umbilical cord to the liver and splits into 3 branches. The blood then reaches the inferior vena cava (IVC). This is a major vein connected to the heart. Most of this blood is sent through 3/ the ductus venosus. This is also a shunt that lets highly oxygenated blood bypass the liver to the inferior vena cava (IVC) and then to the right atrium of the heart. A small amount of this blood goes straight to the liver to give it the oxygen and nutrients it needs.
  Waste products from the fetal blood are transferred back across the placenta to the mother's blood.
  

Inside the fetal heart

• 1/ Blood enters the right atrium. This is the chamber on the upper right side of the heart. When the blood enters the right atrium, most of it flows 2/ through the foramen ovale into the left atrium.
  
• Blood then passes 3/ into the left ventricle. This is the lower chamber of the heart. 4/ Blood then passes to the aorta. This is the large artery coming from the heart.
  
• From the aorta,5/ blood is sent to the A/ heart muscle itself and to B/ the brain and C/ arms. After circulating there, the blood 6/ returns to the right atrium of the heart through the (SVC) superior vena cava. 7/ Very little of this less oxygenated blood mixes with the oxygenated blood. Instead of going back through the foramen ovale, it goes 8/ into the right ventricle.
  
• This less oxygenated blood is 9/ pumped from the right ventricle into the pulmonary artery. A small amount of the blood 10/ continues on to the lungs. Most of this blood is 11/ shunted through the ductus arteriosus to the descending aorta. This blood then 12/ enters the umbilical arteries and flows into the placenta. 13/ In the placenta, carbon dioxide and waste products are released into the mother's circulatory system. 14/ Oxygen and nutrients from the mother's blood are released into the fetus' blood.
  

At birth, the 1/ umbilical cord is clamped and the baby no longer gets oxygen and nutrients from the mother. 
With the first breaths of life, 2/ the lungs start to expand. As the lungs expand, 3/ the alveoli in the lungs are cleared of fluid. 4/ An increase in the baby's blood pressure and a major 5/ reduction in the pulmonary pressures : 6/ reduce the need for the ductus arteriosus to shunt blood. 7/ These changes help the shunt close. These changes 8/ raise the pressure in the left atrium of the heart. They also 9/ lower the pressure in the right atrium. 10/ The shift in pressure stimulates the foramen ovale to close.

Blood circulation after birth

The closure of the ductus arteriosus, ductus venosus, and foramen ovale completes the change of fetal circulation to newborn circulation.
https://www.stanfordchildrens.org/en/topic/default?id=fetal-circulation-90-P01790

Amniotic fluid

10-week-old human fetus surrounded by amniotic fluid within the amniotic sac
he amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products between mother and fetus. For humans, the amniotic fluid is commonly called water or waters (Latin

Development

Amniotic fluid is present from the formation of the gestational sac. Amniotic fluid is in the amniotic sac. It is generated from maternal plasma, and passes through the fetal membranes by osmotic and hydrostatic forces. When fetal kidneys begin to function around week 16, fetal urine also contributes to the fluid.^[1] In earlier times, it was believed that the amniotic fluid was composed entirely of excreted fetal urine.
The fluid is absorbed through the fetal tissue and skin.^[2] After 22 to 25 week of pregnancy, keratinization of an embryo's skin occurs. When this process completes around the 25th week,^[2] the fluid is primarily absorbed by the fetal gut for the remainder of gestation.^[1]

Contents

At first, amniotic fluid is mainly water with electrolytes, but by about the 12–14th week the liquid also contains proteins, carbohydrates, lipids and phospholipids, urea, and extracellular matrix (ECM) components including collagens and glycosaminoglycans, including hyaluronic acid and chondroitin sulfate, all of which aid in the growth of the fetus.

Volume

The volume of amniotic fluid changes with the growth of fetus. From the 10th to the 20th week it increases from 25 to 400 millilitres (0.88 to 14.08 imp fl oz; 0.85 to 13.53 US fl oz) approximately.^[3] Approximately in the 10th–11th week, the breathing and swallowing of the fetus slightly decrease the amount of fluid. Neither urination nor swallowing contributes significantly to fluid quantity changes until the 25th week when keratinization of skin is complete; then the relationship between fluid and fetal growth stops. It reaches a plateau of 800 millilitres (28 imp fl oz; 27 US fl oz) by the 28-week gestational age. The amount of fluid declines to roughly 400 millilitres (14 imp fl oz; 14 US fl oz) at 42 weeks.^[3] Some sources indicate about 500 to 1,000 millilitres (18 to 35 imp fl oz; 17 to 34 US fl oz) of amniotic fluid is present at birth.^[1][4]

Rupture of membranes

The forewaters are released when the amnion ruptures. This is commonly known as "water breaking". When this occurs during labour at term, it is known as "spontaneous rupture of membranes". If the rupture precedes labour at term, however, it is referred to as "pre-labour rupture of membranes". Spontaneous rupture of membranes before term is referred to as "premature rupture of membranes". The majority of the hindwaters remain inside the womb until the baby is born. Artificial rupture of membrane (ARM), a manual rupture of the amniotic sac, can also be performed to release the fluid if the amnion has not spontaneously ruptured.^[5]

Function

Swallowed amniotic fluid (in later stages of development) creates urine and contributes to the formation of meconium. Amniotic fluid protects the developing fetus by cushioning against blows to the mother's abdomen, allowing for easier fetal movement and promoting muscular/skeletal development. Amniotic fluid swallowed by the fetus helps in the formation of the gastrointestinal tract. It also protects the fetus from mechanical jerks and shocks. The fetus, which develops within a fluid-filled amniotic sac, relies on the placenta for respiratory gas exchange rather than the lungs. While not involved in fetal oxygenation, fetal breathing movements (FBM) nevertheless have an important role in lung growth and in development of respiratory muscles and neural regulation. FBM are regulated differently in many respects than postnatal respiration, which results from the unique intrauterine environment. At birth, the transition to continuous postnatal respiration involves a fall in temperature, gaseous distention of the lungs, activation of the Hering-Breuer reflex, and functional connectivity of afferent O2 chemoreceptor activity with respiratory motoneurons and arousal centers.^[
https://en.wikipedia.org/wiki/Amniotic_fluid

The Hering–Breuer inflation reflex, named for Josef Breuer and Ewald Hering, is a reflex triggered to prevent the over-inflation of the lung. Pulmonary stretch receptors present on the wall of bronchi and bronchioles of the airways respond to excessive stretching of the lung during large inspirations. Wikipedia


https://www.google.com/search?client=firefox-b-d&q=Hering-Breuer+reflex