Chapter 42: Preterm Birth

Question 1

Define:
A. SGA
B. LGA
C. Low birthweight
D. Very low birthweight
E. Extremely low birthweighr

Answer 1

SGA <10th percentile
LGA >90th percentile
LBW 1500-2500g
VLBW 1000-1500g
ELBW 500-1000g

Question 2

Define:
A. Early preterm
B. Late preterm
C. Early term
D. Term

Answer 2

Early PT <33 6/7 wks
Late PT 34-36 wks
Early term 37-38 6/7 wks
Term 39-40 6/7wks

Question 3

True or False.

Newborns born before 37 weeks suffer various morbidities, largely due to organ system immaturity.

Answer 3

True

Question 4

After achieving a birtheeighht of _______ grams or a gestational age of ____ weeks for females or ____ weeks for males, survival rates reach 95%.

Answer 4

After achieving a birtheeighht of >= 1000 grams or a gestational age of 28 weeks for females or 30 weeks for males, survival rates reach 95%.

Question 5

This term is defined as the lower limit of fetal maturation compatible with extrauterine survival.

Answer 5

Threshold of viability.

Question 6

Active brain development occurs in what trimester?

Answer 6

2nd and 3rd

Question 7

Enumerate morbidities of newborns born during the periviable period (20-26 weeks AOG).

Answer 7

Hypoxic-ischemic injury and sepsis
Intellectual disability
Cerebral palsy
Blindness
Seizure
Spastic quadriparesis

Question 8

True or false.

Retinopathy of prematurity is a long-term ophthalmologic problem among very low birthweight infants.

Answer 8

False. It is a short term problem.

Long term problems include: blindness, retinal detachment, myopia and strabismus.

Question 9

True or false.

Delivery before 23 weeks typically results in death, and survival rates approximate only 10%.

Answer 9

False.

Delivery before 23 weeks typically results in death, and survival rates approximate only 10%.

Additional info:
For those who live, morbidity is universal.
Those born <25weeks are believed to be specially susceptible to brain injury

Question 10

Enumeration.
The obstetric care consensus document addresses management ootions based on the clinical caharacteritics of a given pregnancy. Enumerate monmodifiable and potentially modifiable factors.

Answer 10

Nonmodifiable factors:
Fetal gender
Fetal weight
Plurality

Potentially modifiable factors:
Location of delivery
Intent to intervene by CS or induction
Corticosteroids
Magnesium sulfate

Question 11

According to the Obsteteic Care Consensus, when should CS delivery be considered for fetuses at:
A. 23-24 weeks?
B. Below 20 weeks?

Answer 11

Consider CS at:
23-24wks for fetal indications
Below 22 weeks for maternal indications.

Additional Info:
In Parkland Hospital, CS delivery for fetal indications are practiced in women at 25 weeks and beyond.
At 24 weeks, CS delivery is not offered unless EFW is at 750g or greater.

Question 12

Distribution of preterm births by gestational age.

Answer 12

34-36wks: 71.3%
32-33wks: 12.1%
28-31wks: 9.5%
27wks and below: 7.1%

Question 13

80% of late preterm births are due to:

A. Spontaneous labor and PPROM
B. Hypertension
C. Abruptio placenta
D. Placenta previa
E. Fetal complications

Answer 13

A.

Soontaneous labor 45%
PPROM 35%
Hypertension 13%
Fetal complications 2%
Abruptio 1%
Previa 1%
Others 3%

Question 14

Enumerate:

4 direct causes of preterm births.

Answer 14

Preterm labor with intact BOW (40-45%)
PPROM (30-35%)
Maternofetal indications (30-35%)
Twins and higher-order multifetal births

Question 15

All of the following are major causes of spontaneous preterm labor, EXCEPT:

A. Maternal-fetal stress
B. Multifetal gestation
C. Premature cervical changes
D. Infection
E. Uterine distention

Answer 15

B. Multifetal gestations

4 Major Causes of spontaneous preterm labor:
Uterine distention
Maternal-fetal stress
Premature cervical changes
infection

Question 16

All of the following are upregulated during labor and contributes to uterine distention, EXCEPT:
A. Contraction-associated proteins (CAPs)
B. Estriol
C. Stretch-induced potassium channel (TREK-1)
D. Gastrin-releasing peptides (GRPs)

Answer 16

C. TREK-1

• upregulated during gestation, downregulated during labor
• potential role in uterine relaxation during pregnancy

Additional Info:

CAP genes that are influenced by stretch include those that code for gap junction proteins like connexin 43, oxytocin receptors and prostaglandin synthase.

GRPs are increased with stretch and promote myometrial contractility.

During maternal stress, maternal serum levels of placental-derived CRH is elevated, raising adult and fetal adrenal steroid hormone production leading to early loss of uterine quiescence.

Question 17

Enumerate.

Mechanisms by which maternal-fetal stress translate to preterm birth. (2)

Answer 17

Activation of placental-adrenal endocrine axis

Premature cellular senescence
Aging of fetal and decidual cells precipate release of uterotonic signals for uterine activation at term.

Question 18

True or false: Cervical Dysfunction

1. In most cases, premature cervical remodeling precedes premature labor onset.
2. Reduction of mechanical competence of the cervix due to genetic mutations of collagen and elastic fiber components may cause cervical dysfunction.
3. Group B streptococcal colonization enhance risk of preterm birth by screting hyaluronidase.

Answer 18

All are true.

Hyaluronidase degrades hyaluronic acid in the cervicovaginal epithelia which aids in bacterial ascension.

Question 19

Bacteria can gain access to intrauterine tissues through the following, EXCEPT:

A. Transplacental transfer of infection
B. Retrograde flow of infection into the peritoneal cavity via fallopian tubes
C. Ascending infection
D. NOTA

Ffup question:
Which is the most common route?

Answer 19

D. NOTA

Ascending infection is the most common entey route.

Question 20

This is inflammation in the absence of detectable intraamnionic microorganisms.

Answer 20

Sterile intraamnionic infection

Question 21

True or false.

The earliier the onset of preterm labor, the lesser the likelihood of underlying infection.

Answer 21

False.

The earliier the onset of preterm labor, the greater the likelihood of underlying infection.

At term, the amnionic fluid is infiltrated by bacteria as a consequencr of labor, whereas in preterm, bacteria represent an inciting cause of labor.

Question 22

Enumeration.

Microorganisms frequently detected in the amnionic fluid of women in preterm labor.

Answer 22

Gardnerella vaginalis
Fusobacterium
Mycoplasma hominis
Gardnerella urealyticum

Question 23

True or false.

The diversity and richness of microbe populations are increased during pregnancy and become less stable.

Answer 23

False.

The diversity and richness of microbe populations are REDUCED during pregnancy and become MORE stable.

Question 24

Which of the following is a risk factor for PPROM?

A. Body mass index >19.8
B. Alcohol consumption
C. Lower socioeconomic status
D. Obesity

Answer 24

C. Lower socioeconomic status

Associated Risk factors for PPROM:
Low socioeconomic status
BMI <19.8
Cigarette smoking
Nutritional deficiencies

Question 25

This trial showed that birth defects were associated with preterm birth and low birthweight neonates.

Answer 25

FASTER trial

First and Second Trimester Evaluation Risk

Question 26

Deficiencybof this bitamin is associated with preterm birth.

A. Vitamin A
B. Vitamin B
C. Vitamin C
D. Vitamin D

Answer 26

C. Vitamin C

Question 27

Intervals of less than _____ months and more than ____ months were associated with greater risk for both preterm birth and SGA newborns.

Answer 27

Intervals of less than 18 months and more than 59 months were associated with greater risk for both preterm birth and SGA newborns.

Question 28

Which of the following is the most important riak factor for preterm labor?

A. Infection
B. Maternal age
C. Multifetal gestation
D. Short stature
E. Prior preterm birth

Answer 28

E. Prior preterm birth

Additional info:
Recurrent preterm delivery risk for prior preterm birth is threefold.
Recurrent births occur with 2 weeks of AOG of prior preterm delivery.
Causes of prior preterm delivery also recur.
Prior indicated preterm birth is strongly associated with subsequent spontaneous preterm birth.

Question 29

Enumeration.

Factors that influence risk of recurrent preterm birth. (3)

Answer 29

Frequency of prior preterm deliveries
Severity as measured by AOG
Order by which preterm delivery occurred

Question 30

Bacterial Vaginosis

________ is to relative concentrations of bacterial morphotypes as ________ is to clinical assessment.

Answer 30

Nugent score

Amsel criteria

Question 31

Which of the following are associated with development of bacterial vaginosis? May have more than one answer.

Chronic stress
Frequent douching
Ethnicity
TNF-a genotype

Answer 31

All are associated.

Question 32

True of fetal fibronectin:

A. Values exceeding 30ng/mL are considered positive.
B. It is present in high concentrations in amnionic fluid and in fetal blood.
C. It functions in intercellular adhesion during implantation and in maintenance of placental adherence to uterine decidua
D. It may be used solely for screening preterm labor.

Answer 32

C.

Fetal fibronectin
Values exceeding 50ng/mL are considered positive.
It is present in high concentrations in amnionic fluid and in MATERNAL blood.
It functions in intercellular adhesion during implantation and in maintenance of placental adherence to uterine decidua
It is used in conjunction with cervical length measurement.

Question 33

Why is transvaginal UTZ better than transabdominal when assessing cervical length?

Answer 33

It is not affected by:
Maternal obesity
Cervical position
Shadowing from the fetal presenting part