Normal First Trimester

1. Normal First Trimester Fetal Biometry Workshop Day 1

2. Objectives • Describe maternal & fetal early OB • Placenta & Fetal Membranes • Normal Sonographic Anatomy & Landmarks • 1st Trimester Assessment & dating

3. Terminology • Conceptual age • Gestational age / Menstrualage • Trimester • Embryonic phase

4. Trimesters • 1st Trimester is 0-12 weeks • 2nd Trimester is 13-28weeks • 3rd Trimester is 28 - 40 weeks • Post dates = after due date

5. Indications 1st Trimester • To confirm presence of intrauterine pregnancy • To evaluate a suspected ectopic pregnancy • To define cause of vaginal bleeding • To evaluate pelvic pain • To estimate gestational [menstrual] age • To diagnose or evaluate multiple pregnancy • To confirm cardiac activity • As an adjunct to chorionic villus sampling, amniocentesis, embryo transfer, IUCD removal • To evaluate maternal pelvic masses and/or uterine abnormalities • To evaluate suspected hydatidiform mole

6. Patient History Taking • Patient age • LMP – normal or not • Symptoms • Pelvic Procedures • Reproductive History • Gravidity • Parity • G3P1012

7. Lab Tests Urine Blood MSAFP Alpha feto protein, serum blood Maternal blood & amniotic fluid Produced by yolk sac, then fetal liver Done 15-22 wks hCG Human chorionic gonadotropin Placental trophoblast cells Blood test most accurate • Detects HCG in urine • positive or negative • Urinalysis throughout the pregnancy

8. Early Development

11. Implantation Sites • Normal • Upper corpus • Fundal region • Ectopic • Fallopian tubes [97%] • Uterine cornua [2.5%]] • Non-tubal sites • Ovaries • Cervix • Abdomen

12. Early Intrauterine Gestation • Decidual Reaction Cast • Non-specific finding 3-4 weeks • Focal echogenic thickening of decidua • Thick endometrium tissue

13. Early Intrauterine Gestation • Decidual Cyst • Not always visualized • 2 to 5 mm fluid collection • No echogenic border • Association with or before normal intrauterine gestation

14. Early Intrauterine Gestation • Implantation Bleed • May follow implantation due to erosion of uterine lining • Hypoechoic cleft in decidua near sac

15. Intradecidual sign • Gestational sac within the decidua abutting the endometrial canal • Should always be seen when maternal serum -hCG is 1700-2000 mIU/mL

16. Double Decidual Sign

17. Double-decidual sign

18. DDS [double decidual sign] • 2 concentric hyperechoic rings adjacent to gestational sac • Inner • decidua capsularis / smooth chorion • Outer • decidua parietalis / developing placenta • Sonolucent center • fluid-filled chorionic cavity

19. Gestational Sac • 1st reliable indicator of IUP • 2 separate fluid filled compartments • Amniotic & chorionic • Yolk sac & embryo • Implants in uterine fundus • Rounded in shape

20. MSD + hCG • 5 mm MSD = hCG of 1800 mU/ml • Continue to increase proportionally

21. MSD

22. Vitteline Duct • Yolk stalk, omphalomesenteric duct • Provide blood flow to YS • Fuses at 7-8 weeks • Arteries then provide blood flow for foregut, midgut, and hindgut. • Vitteline vein drain into the sinus venosus • 3 paired vitteline veins

23. Yolk sac sign • Visualization of the yolk sac within the gestational sac • Yolk sac often seen when MSD is 5-6 mm and always seen when MSD is 8mm

24. Yolk Sac • Within chorionic sac • MSD • 10 mm TV • 20 mm TA • 42 days or 6 menstrual weeks

25. MSD & Yolk Sac

27. Early Intrauterine Gestation • Embryonic Pole • 1st appearance of fetus • ~ 45 menstrual days • Straight echogenic line

28. Gestational Sac Size MSD = Length + Width + Height / 3 Yolk Sac Size Seen in MSD of 10 to 15 mm Crown-rump length Embryo @ longest length Gestational Age

30. Predicting Viability • Cardiac activity • Heart rate • Bradycardia – 1st trimester demise • Lower limits of normal 100 bpm [<6.2 wks] • Lower limit of normal 120 bpm [6.3 -7 wks] • Gestational Sac size • Small – poor outcome • MSD - CRL mm > 5 mm; if < poor outcome • Yolk Sac • Size [large or small] & shape

31. Cardiac Activity

32. Embryo at 7 to 9 Weeks • Early umbilical cord • Connecting stalk attaches embryo to developing placenta [chorion frondosum] • Early development of limbs, midgut & CNS • Large rhombencephalic cavity in head

33. Embryo at 9 to 12 Weeks • Developing anatomy visualized • Extremities develop • >11 weeks bowel returns to abdominal cavity • Fetal calvarium well formed [12 weeks] • Lateral ventricles contain prominent choroid

34. Placenta & Membranes

35. Placental Development

36. 1st Trimester - Placental Growth • Forms from chorionic villi • Visible at 7 to 8 weeks’

38. Structural Abnormalities • Earliest time abnormality can be detected • Earliest time abnormality should be detected • 1st trimester: • Omphalocele • Duodenal atresia • Ocular defects • Cardiac defects • Septated cystic hygromas • Bifid appearance – conjoined twins

39. Growth Evaluation by US

40. Measurements • GS • CRL • BPD • OFD • HC • AC • HC/AC • Femur (humerus, ulna, tibia can be done as well but not routine) • FL/BPD • FL/AC • Fetal weight estimates (need BPD, AC, and FL)

41. Guidelines for Dating 1st Pregnancy

42. Gestational Sac • 100% specific for no Pregnancy • MSD grows about 1mm/day up to 10 weeks gestation • Measure inner to inner • If GS > 25mm and No embryo • If GS > 20mm and No YS • (L x W x H) / 3 = mean sac diameter (MSD) • GA (days) = MSD (mm) +30 • (TA) MSD of 5mm should = 5 wks GA • (TV) MSD of 2-3mm = 4 wks GA • Can not definitively age a pregnancy on MSD alone

43. Gestational Sac

44. CRL measurement

45. BPD - Biparietal diameter

46. BPD - Biparietal diameter

47. OFD – Occipitofrontal Diameter

48. HC - Head circumference • Same view as BPD • Length of outer perimeter of skull • Use ellipse or trace • (D1 x D2) x 1.57

49. Cephalic Index • CI = (shortest axis, BPD/ longest axis, FOD) x 100= 78.3 • Measure outer to outer • Normal mean = 78.3 • Dolicocephalic <70 • Brachycephalic >86