Module 1: Physiology of Fetal/Newborn Transition

Question 1

Describe aspects of fetal lung maturation that influence per viability and viability of the neonate.

Answer 1

The fetal lung requires adequate thoracic space, enough lung fluid, and fetal practice breathing. The lungs develop in stages while receiving oxygen from the placenta/umbilicus.

1st: Airways develop into branches
2nd: terminal alveolar sacs appear between 16-24w.
3rd: saccular stage at 28-36 w, the space between the pulmonary capillaries and alveoli diminishes, alveoli develop and are lined with type I and II alveolar cells. Type II produces and stores surfactant (phospholipid that helps keep the alveoli open during exhalation).
4th: at 36w+ more alveoli form, increasing the surface area for gas exchange. The lungs continue to mature after birth.

After birth: fluid is cleared from the lungs, they expand and circulation path changed increasing pulmonary perfusion.

Question 2

Describe the timing of fetal lung fluid clearance. What could affect this timing?

Answer 2

Fetal lung fluid is secreted in the type II alveolar cells. Before labor begins, the process changes from being fluid secretion to fluid absorption. The fluid level in the lungs begins to decrease by increased production of epithelial sodium channels (ENaC). Water follows Na, and fluid is pulled from the lungs to the interstitial space. The activation of ENaC is associated with gestational age.

Preterm deliveries, inductions, fast labors may lead to inadequate preparation or “preclearing” of the lungs before birth.

Question 3

Differentiate between the biochemical and mechanical events that stimulate the baby to take his/her first breath.

Answer 3

-Biomechanical: hypoxia, hypercapnia, stimulation of chemoreceptors
-Mechanical: Physical stimuli, thoracic squeeze

There are three biochemical events that appear to stimulate the baby’s first breath. As labor progresses the fetus’s PO2 slowly decreases and the PCO2 slowly increases. This physiologic mild hypoxia and hypercapnia that occurs at the end of labor stimulates respiration. The third biochemical event occurs with the clamping of the cord which stimulates peripheral and central chemoreceptors

Mechanical respiratory stimulants excite the respiratory center and include physical stimuli like cooler temperature, gravity, pain, light, noise, and thoracic recoil (the squeeze babies get through a vaginal delivery) that occur with birth.

Question 4

What are the current recommendations on suctioning at birth?

Answer 4

Recommends against routine suctioning due to bradycardia and arrhythmia risk. This includes bulb suctioning!

Expanded explanation: Research has not shown any benefit to routine suctioning (bulb syringe or a suction catheter). Suctioning may cause severe arrhythmias in up to 15% of term neonates including profound bradycardia. Some studies have found a longer time to reach optimal O2 saturation among those who have been suctioned (Graves & Haley, 2013). According to the 2015 Neonatal resuscitation guidelines, consideration of suctioning immediately following birth should be reserved for those infants whose airway appears obstructed or if positive pressure ventilation is indicated. Consequently allowing the oropharyngeal fluid to clear naturally and gently wiping the fluid and mucus away is sufficient for most newborns.

Question 5

**Describe basic fetal cardiac development. What is the most critical timeframe of fetal development?

Answer 5

As embryonic folding starts, the two endocardial tubes are pushed into the thoracic cavity, where they begin to fuse together, and this is completed at about 22 days. At around 18 to 19 days after fertilization, the heart begins to form. The heart begins to develop near the heed of the embryo in the cardiogenic area. The embryonic period is the most critical period of development because of the formation of internal and external structures.

Question 6

What is the pathway of fetal circulation?

Answer 6

Blood travels from the placenta to the baby via the: umbilical vein. From the umbilical vein, blood travels through the ductus venosus then on to the…inferior vena cava. From the inferior vena cava, blood flows into the right atrium. Blood flows from the right to left atrium via the foramen ovale. Blood flows from the right ventricle to the pulmonary arteries. Only a small amount goes to the developing lungs, due to high pulmonary vascular resistance. From the right ventricle, blood is shunted away through the ductus arteriosus and back to aorta.

Question 7

What are the circulatory changes following birth?

Answer 7

1) At birth, the neonate no longer receives prostaglandin and prostacyclin, causing constriction of the ductus arteriosis (DA). This facilitates the use of the right ventricle and pulmonary arteries for blood flow.
2) The DA functionally closes within 48 hours of birth
4) Clamping of the umbilical cord causes a rise in systemic vascular resistance and a decrease in pulmonary vascular resistance
5) This further encourages the closure of the DA (note the DA is permanently closed by 1-3 months)

Note: the foramen ovale also functionally closes when the systemic resistance is higher than the pulmonary but permanently by 30 months

Question 8

How does an infant maintain and create heat after birth? What does s/he lack that helps to maintain body heat?

Answer 8

Three ways: 1-voluntary muscle activity (moving), 2-shivering, 3-nonshivering thermogenesis

1-Moving: potentially limited due to muscle strength
2-Shivering: only seen in severe cold stress
3-Non-shivering therm.: aka use of Brown fat for heat production. Brown fat is a nonrenewable source used for heat production. Using glucose, the brown fat breaks down to create heat that circulates the neonate. In the cases of hypoglycemia and thyroid dysfunction, this does not function properly

Question 9

It is best to keep newborns in a neutral thermal environment as they can lose heat through 4 mechanisms. What are they? How can the midwife be prepared to reduce or minimize heat loss?

Answer 9

Convection, conduction, radiation, evaporation.

Best way to prevent is skin to skin and dry baby!
You can also raise the room temp, use warm blankets and hat, ensure baby is dry, keep away from cold walls.

Question 10

Describe heat loss through convection and how to prevent it.

Answer 10

Heat loss through the movement of air across the body. Ex. A/C or a fan on

Prevent: increase the room temp

Question 11

Describe heat loss through conduction and how to prevent it.

Answer 11

Heat loss from direct contact/physical contact w/cooler surface, wet clothing

Make sure mom’s chest/gown is dry, and the towel is dry. Do not place the baby on a cold surface. Skin to skin with mom will heat baby!

Question 12

Describe heat loss through radiation and how to prevent it.

Answer 12

Heat loss through infrared rays via NO direct contact: walls, windows, heat lamps.

Prevent: keep baby away from window during the winter

Question 13

Describe heat loss through evaporation and how to prevent it.

Answer 13

Heat loss from conversion of water to gas

Prevent by drying the baby

Question 14

Describe the ways a healthy newborn maintains his/her glucose levels, including the role of glycogen, gluconeogenesis, and lipids.

What types of babies may not be able to maintain their glucose?

Answer 14

Baby maintains glucose 3 ways: 1-breast milk/formula, 2-glycogen stored in the liver (glycogenolysis), 3-gluconeogenesis (making glucose)

Baby’s glucose begins to drop after delivery because they are no longer receiving it from the mom. After delivery, brown fat is oxidized to warm the body. This requires the use of glucose.

Glycogen is also stored in the liver prior to birth (most storage occurs in the third trimester)

Babies that may not be able to maintain: Premature due to less brown fat and less stored glycogen, LGA babies due to larger surface area and food requirements, sga due to less brown fat, cold babies due to quick use of brown fat (using a lot of energy to warm themselves)

Question 15

Describe the conjugation and de-conjugation of bilirubin.

Answer 15

Indirect (Unconjugated) vs. Direct (conjugated)

Due to the short lifespan of newborn RBCs (80d), decreased UGT (protein that conjugates billi) and an immature liver, newborns have more byproducts of the RBC breakdown (i.e. billirubin). RBCs break down to unconjugated billirubin which binds to albumin. If there is too much billirubin and the albumin becomes overwhelmed, hyperbilirubinemia can occur where the extra billirubin settles in the skin, organs, and adipose tissue. When the system is functioning properly, unconjugated billirubin become conjugated in the liver where the majority of it is deposited in bile and excreted through both stool and urine. A small amount is recycled within the body.

-Indirect bilirubin=unconjugated bilirubin=fat soluble
-Direct bilirubin=conjugated bilirubin=water soluble
-Direct bilirubin can be deconjugated back to indirect bilirubin

Question 16

Describe the physiologic changes in the newborn urinary system in the first 3-4 days of life and the risks of this immature system to the baby.

Answer 16

The newborn renal system is immature and has less renal blood flow and a lower glomerular filtration rate. This can lead to sodium losses and electrolyte imbalances.

95% of babies void within the first 24 hours of life but some void within the first 48 hours. They may only void 30-60 cc in that time. They should not pass protein or blood through the urine.

Question 17

Compare and contrast the newborn digestive system in relation to differences in babies who are breastfed vs. those who are given formula.

Answer 17

Breastfed babies receive a natural laxative through colostrum, so they are more likely to begin to pass stool. However, they may have more difficulty regulating their glucose because they have to work harder to eat. IgA received from breast milk helps with gut immunity; it lines the small intestine and binds with harmful antigens.

Formula-fed babies do not have to work as hard to eat, so they may eat more than their stomach can hold (30cc) and be more prone to reflux.

Question 18

Describe gut closure

Answer 18

Gut closure is the process by which the epithelial surfaces of the intestine become impermeable to antigens. Prior to gut closure, the infant is vulnerable to bacterial/viral infection as well as to allergenic stimulation through intestinal absorption of large molecules. In the breastfed newborn, maternal secretory IgA restricts immune activation and bacterial attachments.

Question 19

How does the newborn immune system differ from that of the adult?

Answer 19

Newborns primarily rely on passive immunity.

Expanded explanation: The neonatal immune system is immature in a number of ways, including having incomplete physical and chemical barriers in the GI system. Innate immunity is the primary line of defense for the neonate.

Question 20

Explain the difference between passive and active immunity. Give examples for a newborn.

Answer 20

Passive immunity is where one receives antibodies to an antigen (Ex. receiving IgA through the breast milk to protect the gut, the Hep B vaccine received after birth)

Active immunity is where one is introduced to a pathogen/antigen and must create their own antibodies

Question 21

Describe the effects on the newborn with timing of cord clamping.

Answer 21

30-50% of a baby’s blood volume is received by placental transfer from delayed cord clamping. It has been shown to affect the initial H/H of a baby. The amount of time before the blood flow stops varies. It is recommended to DCC for 1-3 minutes, but if the baby is on the mother’s chest, it may take up to 5 minutes (2 if the baby is below the level of the placenta). DCC increases the level of iron storage but may contribute to rates of hyperbilirubinemia and need for phototherapy.

There are no studies on the benefits of DCC in relation to C/S, but the recommendations are to milk the cord if DCC is not possible.

Question 22

Describe physiologic jaundice and its times of peak and onset.

Answer 22

Jaundice due to these normal newborn conditions of elevated bilirubin is called physiologic jaundice, and it typically appears on the second or third day of life.

Onset: >36 hours
Peaks: 3-4 days (formula fed) & 5-7 days (breastfed)
Peak serum total bili: 5-12 mg/dl (formula fed) & 7-14 mg/dl (breastfed)

Question 23

Describe breastfeeding associated jaundice and its times of peak and onset.

Answer 23

Breastfeeding jaundice most often occurs in the first week of life when breastfeeding is being established. Newborns may not receive optimal milk intake, which leads to elevated bilirubin levels due to increased reabsorption of bilirubin in the intestines (aka bilirubin becomes de-conjugated)

Onset: 2-4 days
Peak: 3-6 days
Peak total bili: >12 mg/dl

Question 24

Describe breast milk jaundice and its times of peak and onset.

Answer 24

The exact etiology is unknown, but this jaundice is associated with breastfeeding. It can be differentiated from breastfeeding jaundice by how long it lasts. I often persists past three weeks of life and may resolve spontaneously even if breast feeding continues.

Onset: 4-7 days
Peak: 5-15 days
Peak total bili: >10 mg/dl

Question 25

What is the optimal range of hematocrit for a newborn?

Answer 25

43-63%

Question 26

What is the optimal range of hemoglobin for a newborn?

Answer 26

14-20 g/L

Question 27

What is the optimal range of WBC for a newborn?

Answer 27

10,000-30,000/mm^3

Question 28

What is the optimal range of platelets for a newborn?

Answer 28

150,000-400,000

Question 29

When would jaundice likely be considered pathologic?

Answer 29

Jaundice is considered pathologic if it presents within the first 24 hours after birth, the total serum bilirubin level rises by more than 5 mg per dL (86 mol per L) per day or is higher than 17 mg per dL (290 mol per L)