OB
GUIDELINES
Lexicon for First Tri US. SRU Consensus 2024.pdf
FIRST TRIMESTER PREGNANCY
FIRST TRIMESTER PREGNANCY FINDINGS.pptxTimeline:
Gestational sac is first seen at 5-5.5 weeks via TVUS if beta-hCG >2000 mIU/mL. Though, there are exceptions.
Yolk sac becomes visible at 5.5 wks GA
Fetal pole and heart motion become visible at 6 weeks GA
Physiologic gut herniation begins 6-8 weeks GA
Embryo shows features and rhombencephalon(forming brain stem; round anechoic structure in posterior brain) forms 8-10 weeks GA
Physiologic gut herniation completes 12-13 weeks GA
Amnion fuses w chorion at 14 weeks GA
Any round or oval fluid collection in the uterus in setting of positive pregnancy test & normal adnexa is overwhelmingly likely to represent a very early intrauterine pregnancy (IUP). Unlikely to represent decidual cyst or pseudo-gestational sac which can be seen in ectopic pregnancies.
Gestational sac should be round/oval, well defined and smooth with decidua >2mm. Anything else is suspicious.
Mean sac diameter (MSD) is the avg diameter of the gestational sac measured in three orthogonal planes (LxWxH/3). It is not routinely measured but may be helpful in assessing viability.
MSD should be >= 5mm larger than the CRL at less than 9 weeks. If less, poor outcomes!
If GS >8 mm by TVUS, a yolk sac should be visible. If yolk sac is not present, the pregnancy is unlikely to be successful.
If MSD measures 16-24 mm a live embryo should be visible. If not seen, the pregnancy is suspicious for but not diagnostic of failed pregnancy.
If MSF >24 mm or greater and no embryo is seen = failed pregnancy.
Yolk sac appears after gestational sac:
Gradually enlarges until 10 weeks GA, measuring up to 5-6 mm.
Starts to shrink >10 weeks GA and is no longer visible >14 weeks GA.
FHR <90 bpm carries dismal prognosis.
Physiologic herniation of bowel: abd wall mass at based of umbilical cord; 4-7 mm in fetus w CRL of 19-41 mm.
Should not be present after 12-13 weeks or be seen with CRL >44mm.
PREGNANCY DATING
Between 5-6 weeks, gestational age is determined based on 3 typical appearances of early pregnancy:
Gestational sac only: 5 weeks
Gestational sac w/ yolk sac w/o embryo: 5.5 weeks
Gestational sac w/ embryo <3mm and heart beat: 6 weeks
For embryo's >3 mm in length, the CRL is used to assign gestational age using established reference tables.
CRL is used to estimate gestational age up to 12 - 14 weeks
>12 -14 weeks, dating is estimated using multiple fetal measurements (BPD, abd/head circumference, femur length) to determine arithmetic US age.
At GA 8 6/7 weeks or less (based on LMP), US dating should be used if LMP dating and US dating differ by >5 days.
At GA 9 0/7 weeks - 13 6/7 weeks (based on LMP), US dating should be used if LMP dating and US dating differ by >5 days.
The only ways to reliably know a preceise gestational age are if a previous US was performed to establish dating or patient underwent IVF w known embryo transfer date:
Gestational age is calculated from first day of the last menstrual cycle
If IVF w known implantation date, 2 weeks are added to be consistent with spontaneous pregnancies.
beta-hCG REVIEW
BhCG levels peak at 9-11 weeks after which they decline.
Avg doubling time of BhCG levels in a normal viable IUP is approx 48 hours
<50% rise in 48 hrs is almost always a nonviable pregnancy (Intrauterine or extrauterine)
Ectopic pregnancies may manifest w abnormal rise, fall or early plateau of BhCG.
PERIGESTATIONAL HEMORRHAGE
SUBCHORIONIC HEMORRHAGE
Complication of early pregnancy 2/2 bleeding of the chorionic attachment -> blood collects b/n the chorion and uterine wall. Vaginal bleeding may occur if the blood leaks to the cervical canal. Outcomes are dependent on size of hemorrhage, maternal age, and GA of the fetus.
Imaging:
Crescentic collection of variable echotecture that elevates the chorionic membrane.
Echotexture
Acute: hyperechoic (sometimes difficult to delineate from chorion)
Subacute to chronic: decreasing echogenicity over time.
Size
Small: <1/3 of chorion
Medium: 1/3 - 1/2 of chorion
Large: >2/3 of chorion
RETROPLACENTAL HEMATOMA
Hematoma that separates the placenta from the uterine wall.
Spiral arteries are likely source of bleeding
Placental abruption is reserved for after 20 weeks GA.
50% fetal demise.
SUBAMNIOTIC HEMATOMA
Hematoma between amnion and chorion that is limited by amnionic reflection at placental insertion site of umbilical cord. Rare entity. Rupture of chorionic vessles.
VIABILITY
Must distinguish between
Findings definitive for pregnancy failure
Findings suspicious but not definitive for pregnancy failure, which will require follow-up testing to establish a definitive dx.
PREGNANCY FAILURE
Criteria most often used to diagnose pregnancy failure:
Absence of cardiac activity by time embryo is certain length
Absence of embryo by the time a gestational sac has grown to certain size. Referred to as anembryonic pregnancy or blight ovum.
Absence of embryo after a certain point in time.
IUP of UNCERTAIN VIABILITY
If intrauterine gestational sac does NOT show embryonic heartbeat or definitive findings of pregnancy failure, the pregnancy is considered to be of uncertain viability
If there is suspicion of pregnancy failure, a follow up US performed in 7-10 days to reassess viability is generally appropriate.
RPOC is retained placental or trophoblastic tissue; occurs after delivery or termination of pregnancy. Presents w/n few days or up to 6 weeks post delivery/abortion.
The presence of RPOC differentiates a complete miscarriage from an incomplete miscarriage. RPOC patients often present w postpartum hemorrhage.
RPOC occurs more frequently in cases of medical termination of pregnancy and second trimester miscarriage.
Tx: PGE1 analogs, dilation and curettage, hysteroscopic removal.
Findings
Thickened endometrial echo complex ≥ 10 mm, or echogenic endometrial mass + internal vascularity
Less likely if EEC < 10 mm in thickness and avascular
Solid, heterogeneous or echogenic endometrial/intrauterine mass
Irregular interface b/n endometrium and myometrium
Intrauterine fluid is common.
Color doppler: degree of vascularity varies from hypo- to markedly hypervascular
Vascularity typically extends from adjacent myometrium to endometrial component.
Markedly hypervascular RPOC may mimic AVM though vascularity is centered in myometrium. Increased risk of severe bleeding following D&C possibly 2/2 unroofing a large vessel.
Avascular RPOC may mimic clot. Absence of flow does NOT exclude RPOC (can present w clot or avascular POC)
DDX
Normal postpartum uterus:
Variable endometrium: smooth or irregular
Small echogenic foci and fluid is common.
Foci of gas can be seen up to 3 weeks post partum
Endometrial thickness <2cm initially and should decrease to <8mm w uterine involution.
Uterine atony for immediate PPH
Atony = normal appearing cavity
RPOC: thickened endometrial echo complex or mass
Intrauterine blood/clot
Avascular and typically more hypoechoic than RPOC.
changes or resolves on FU scans
Enhanced myometrial vascularity (uterine non-AVM)
Marked vascularity (involuting peritrophoblastic tissue) over full thickness of myometrium related to involution of placental bed after pregnancy and miscarriage.
Occurs in 50% of normal postpartum patients at day 3
Disappears spontaneously.
AVM
Typically has no focal endometrial mass.
MUST see early venous drainage on angio, MR, CT
Dilated tangle of vessels w arterial to venous communication isolated to myometrium. Vascularity does NOT extend to endometrium and is centered in myometrium. Uterine non-AVM can have similar appearance.
Hypervascular RPOC often misdiagnosed as uterine AVM.
Most develop 2/2 uterine tissue injury usually from prior D&C; serum beta-hCG is usually negative or minimal.
Endometritis
Clinical diagnosis of infected endometrium; typically no sonographic correlate. Can have both RPOC and coexisting endometritis.
Histed_36.7.pptxECTOPIC PREGNANCY
95% are located in the fallopian tube.
RF:
Prior ectopic pregnancy
Tubal injury
PID
Salpingitis isthmica nodosa
Endometrial injury or congenital anomalies
IUD use
Findings
Adnexal mass separate from ovary. adnexal mass may not be detected on TVUS in 15-35% of patients.
Ring of fire sign: peripheral hypervascularity; nonspecific and can be seen w corpus luteal cysts.
Echogenic fluid w/n Morrison pouch and the cul-de-sac should raise concern for ruptured ectopic w/ 86-93% PPV.
Absence or presence of FF is not reliable indicator to exclude tubal rupture
Heterotopic pregnancy:
Rare in general population; coexistence of an IUP and ectopic preganancy. Not uncommon in patients w invitro (1-3%)
Interstitial/cornual ectopic:
Occurs when implantation takes place w/n the intramyometrial segment of the fallopian tube. Can manifest later up to 16 weeks GA owing to distensibility of this segment.
Accounts for almost 20% of deaths 2/2 hemorrhage in ectopic pregnancies despite having incidence of 2-6%.
Finding: eccentrically located sac surrounded by thin myometrium (<5mm), interstitial line sign (thin echogenic line connecting the endometrium to gestational sac, representing interstitial portion of fallopian tube.
Cervical ectopic:
Must be distinguished from a miscarriage in progress
Findings: Hourglass appearance of uterus as fetus expands the cervix. Cardiac activity below the internal os.
DDX:
Miscarriage in progress: gestational sac may be noted to change shape or location during or b/n US examinations. Sliding sign: if US transducer can manipulate the gestational sac, it suggests nonadherence to the cervix.
Cesarean scar ectopic: Gestational sac in anterior myometrium w overlying myometrial defect. May also rupture from myometrial thinning along the C scar.
Ovarian ectopic
Accounts for 3% of ectopics
May be part of a heterotopic pregnancy
Strongly associated w use of an IUD
May be suggested by presence of a gestational sac, chorionic villi or atypical cyst w hyperechoic ring w normal fallopian tube.
Abdominal ectopic
1.3% of ectopic pregnancies.
Occurs w/n the intraperitoneal cavity.
Signficant risk of hemorrhage w maternal mortality >7.7x than other locations.
PREGNANCY OF UNKNOWN LOCATION
Location of a pregnancy cannot be determined (no intrauterine fluid collection and normal/near-normal adnexa, this is considered a PUL. Near-normal adnexa includes corpus luteum, small amount of pelvic free fluid and paratubal cyst.
DDX
Early IUP, failed pregnancy or ectopic pregnancy.
FU BhCG level tests and/or US are recommended in stable patients who desires pregnancy.
GTD
Encompasses benign and malignant forms; all GTDs arise from the placenta.
Consist of hydatidiform moles and choriocarcinoma arising from cellular (villous) trophoblasts.
Syncytiotrophoblasts: digest endometrium to form lacune, produce beta-hCG
Cellular trophoblasts: form chorionic villi.
COMPLETE MOLAR PREGNANCY
Large for date uterine size; snowstorm appearance of endometrium (echogenic mass w hypoechoic foci)
Small (1-30 mm) cysts of varying sizes in the endometrium representing hydropic chorionic villi (cluster of grapes)
Theca lutein cysts in 20% representing large functional ovarian cysts that enlarge the ovaries, may occur secondary to exaggerated ovarian stimulation by the high levels of beta-hCG.
PARTIAL MOLAR PREGNANCY
Can mimic anembryonic pregnancy, miscarriage, or RPOC
Can be difficult to detect; correlation with quantitative beta-hCG is key.
US findings
Gestational sac may appear empty, elongated, or ovoid or contain amorphous echoes
Fetal demis, anomalies, growth restriction.
Oligohydramnios
Enlarged placenta relative to size of the uterus w cystic change.
POST PARTUM
POSTPARTUM COMPLICATIONS.pdfRSNA POSTPARTUM COMPLICATIONS.pptx