1. SON 2121 Obstetrical Sonography I Chapter 6
Ultrasound Evaluation during the first Trimester of Pregnancy
Holdorf
SON 2121 Obstetrical Sonography I Chapter 6

2. Normal First Trimester
Fertilization
On day 14 of the menstrual cycle, the ovum is released and enters the fallopian tube. Fertilization by the sperm cell results in formation of a zygote. Important features of fertilization are as follows:
A mature ovum is released from the Graafian follicle.
The ruptured follicle becomes the corpus luteum, which produces progesterone.
Progesterone and estrogen stimulate endometrial cellular proliferation in preparation for implantation.
Fertilization usually occurs in the ampullary portion of the fallopian tube within hours after ovulation.

3. A sperm penetrates the outer layer (Zona Pellucida) of the ovum.
Genetic material from the sperm fuses with the nucleus of the ovum to produce a single cell (zygote), containing a “set” (23 pairs or 46 total) chromosomes.

4. Cell division begins and results in several early embryonic stages:
GAMETE The male or female reproductive cell, i.e. the ovum or spermatozoa
ZYGOTE the fertilized single-cell organism is called a zygote prior to mitotic division.
MORULA The ball of cells, surrounded by the Zona Pellucida, which is transported through the fallopian tube toward the uterus.
BLASTOCYST An organized collection of cells with a cystic cavity surrounded by trophoblasitc cells; it enters the uterine cavity about 7 days after fertilization. Trophoblasic cells differentiate into an inner cell layer (cytotroblaast) and an outer multicellular layer (syncytotrophoblast). These cells produce hCG which extends the life of the corpus luteum. The corpus luteum, in turn, continues to secrete progesterone which helps assure retention of the endometrial lining.

5. Diagram of Fertilization

6. Fallopian tube demonstrating fertilization and implantation.

7. hCG Levels
Human chorionic gonadotropin (hCG) is a glyco-protein produced by trophoblasitc tissue, which is detectable in maternal serum and urine. It forms the basis of current pregnancy tests. hCG is believed to support the corpus luteum, thereby assuring a continuous supply of progesterone in the first trimester.

8. Corpus luteum not in handouts
“Yellow body” is a temporary endocrine structure that is involved in the production of high levels of progesterone, which in tern further helps in the release of Gonadotropin- releasing hormone (GnRH) and thus the secretion of Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH).
IN SUMMARY- secretes progesterone, which is responsible for the decidualization of the endometrium and its maintenance.

9. Corpus luteum cyst of pregnancy not in handouts

10. hCG Levels cont…
First detected 3 weeks after the LMP (7-10 days after ovulation)
Doubles every 2-3 days
Plateaus around 8-9 weeks, then declines

11. Beta hCG testing can be done two ways
Qualitative urine results are positive or negative
Quantitative results provide specific levels of the protein present in the blood. The most common radioimmunoassay method used is 2IRP, although other methods exist. (Second International Standard 2IS, or Second International Reference Preparation 2IRP

12. Quantitative vs. Qualitative Quantitative Date
Deals with numbers
Data which can be measured
Length, height, area, etc.
Qualitative Data
Deals with descriptions
Data can be observed but not measured
Colors, textures, appearance, etc.

13. hCG levels
Abnormal levels of maternal serum hCG can indicate problems with the developing pregnancy.
Greater than expected levels are associated with
Incorrect dates
Gestational Trophoblasic disease
Multiple gestations
Less than expected levels are associated with
Ectopic pregnancy
Embryonic demise

14. Primitive Germ Layers
In the blastocyst cavity, an inner cell mass is differentiating from a bilaminar disk to a trilaminar embryonic disc. There are three germ cell layers that comprise the embryonic disk by 5 weeks after LMP:
Endoderm: inner layer
Mesoderm: Middle layer
Ectoderm: outer layer

15. The three primitive germ layers

16. Homework Not in handouts
What fetal features arises from the three germ layers?
Endoderm
Mesoderm
Ectoderm

17. From weeks 6 to 10, all major internal and external structures begin to form. The primordial heart begins to beat by 6 weeks GA, but other organ system function remains minimal.

18. Implantation
By the end of the 3rd week LMP, the blastocyst begins to implant in the decidualized endometrium. During this process, as Trophoblastic tissue invades the endometrium, vaginal bleeding may occur. This bleeding may be mistaken as a normal menstrual period.

19. Placental chorionic Villi

20. Trophoblastic tissue

21. Sonographically, three distinct layers of decidualized endometrium are observed:
Decidua capsularis: Closes over and surrounds the blastocyst
Decidua Basalis: Develops where the blastocyst attaches; it contributes to the maternal portion of the placenta
Decidua parietalis (decidua Vera) results from hormonal influence on the uninvolved endometrial tissue.

22. The decidual capsularis and decidua Vera can be seen sonographically as the Double sac sign (DSS) of pregnancy. This DSS is not seen in an ectopic pregnancy, with its corresponding pseudo-gestational sac.

23. Double Sac Sign

24. The DSS double-sac sign

25. Diagram-DSS

26. Placenta
The placenta contains both maternal and fetal tissue. The maternal component is derived from the decidua basalis, and the fetal component is derived from the Trophoblasic tissue. By 5 weeks LMP, the trophoblasts develop into chorionic villi. Those villi in contact with the decidua basalis rapidly increase in number and vascularity to become the chorion frondosum, the fetal part of the placenta.

27. Membranes of the conceptus
What sonographers and sonologists refer to as the chorionic membrane is actually that chorionic villi which surrounded the blastocyst but did not further develop into chorion frondosum. It becomes compressed and avascular, and appears as a “membrane.” The chorionic membrane surrounds the gestational sac and extends up to and merges with the edge of the placenta.

28. The amniotic membrane forms from cells that originated from the inner blastocyst. It initially forms opposite the secondary yolk sac, and is attached to the embryonic disk. The amnion and its cavity grow rapidly to surround the embryo, and it actually remains attached to the embryo at the umbilical cord insertion site.

29. The amnion and the chorion begin to fuse by the middle of the first trimester. Fusion is usually complete by weeks. Sonographic identification of the separation of the two membranes before 16 weeks is a normal finding and is not associated with a poor outcome of the pregnancy.

30. Chorion and amnion fusing

31. Chorion and Amnion

32. Early embryo (8 weeks) in the amnion

33. Hemodynamic Changes
Trophoblastic tissue provides the developing conceptus with nutrients and oxygen. Since embryonic tissue is highly active metabolically, a continuous supply of new blood is necessary. Through the process of angiogenesis and neovascularizaton, a rich network of small blood vessels develops to provide necessary perfusion. The result is high volume, high velocity, and low resistance flow throughout the cardiac cycle. This is represented by Doppler spectral waveforms as high velocity, low resistance flow.

34. Doppler Spectral waveform

35. SONOGRAPHIC ANATOMY Gestational sac
The identification of a gestational sac (GS) within the endometrial cavity is the first sonographic evidence that a normal, intrauterine pregnancy is present. A GS is ALWAYS seen in a normal IUP when the following discriminatory levels are achieved:
Serum Beta hCG > 1,000 mlU/ml (endovaginal using 2IS
Serum Beta hCG >1800 mlU/ml (transabdominal using 2IS
Certain LMP > 5 weeks (with a normal 28 day cycle

36. Round, oval, well defined Echogenic, intact borders
Normal sonographic observations - Gestational sac
Double sac sign
Round, oval, well defined
Echogenic, intact borders
Positioned in the fundus or mid-uterus
Grows roughly 1mm / day
Yolk sac present when MSD is greater than or equal to 13mm

37. Mean Gestational Sac Diameter (MSD)
Mean sac size can be used to date an early first trimester pregnancy. Because several extrinsic factors can alter sac dimensions, MSD is best used prior to the identification of a crown rump length. The gestational sac grows at the rate of 1.1 mm per day.
A mean diameter is calculated from three planar sections:
MSD in mm = (AP + Long + Trans) divided by 3

38. Mean Gestational Sac Diameter MSD) w/ TV probe

39. Gestational Sac

40. Mean Gestational Sac Diameter (MSD)
Endovaginal measurements are more accurate:
MSD – CRL that is less than or equal to 5mm is associated with a high risk of spontaneous abortion.

41. Yolk Sac
The yolk sac is the first structure seen within the gestational sac. With endovaginal ultrasound, the yolk sac can be visible by the beginning of the 5th week LMP, and almost always is seen with the MSD is 8mm. Transabdominally; the yolk sac should be evident by 7 weeks LMP, when the MSD is 20mm.

42. The sonographic appearance of the yolk sac may be helpful in predicting an abnormal outcome:
Diameter > 5.6 mm between 5 and 10 weeks GA
Calcified yolk sacs are only seen with embryonic demise.

43. normal yolk sac TV

44. Abnormally Shaped Yolk Sac

45. Abnormal Yolk sac with Transabdominal approach

46. Crown Rump Length (CRL)
The CRL is the most accurate of all measurements throughout pregnancy, and is accurate for dating within 3-5 days if measured properly. The correct measurement is obtained from the top of the head to the bottom of the rump (excluding legs) Embryonic growth is at the rate of 1mm per day.
Rule of thumb: CRL (mm) + 42 days = GA (days)

47. CRL measurement

48. CRL

49. Embryonic Anatomy
With endovaginal imaging, developing embryonic anatomy is seen much earlier than with transabdominal imaging alone. Some structures initially thought to represent abnormalities have been determined to be normal in the first trimester.

50. Rhombencephalon
The posterior aspect of the fetal crown has a hypoechoic area which is part of the normal development of the central nervous system. This hypoechoic area, the rhombencephalon, is seen in a midline Sagittal view of the embryo, and should not be confused with abnormal dilation of the developing ventricular system (i.e., Dandy-Walker malformation or early ventriculomegaly)

51. the Rhombencephalon

52. Midgut herniation
From approximately 9 to 12 weeks of gestation, the abdominal wall is normally open at the level of the umbilical cord. This allows herniation of the intestinal viscera, where it must undergo midgut rotation before regressing back into the abdominal cavity. AN echogenic bulge outward at the base of the umbilical cord is evident, but this should not be mistaken for a gastroschisis or an omphalocele. Only after 14 weeks of gestation should this herniation be diagnosed as abnormal.

53. midgut herniation prior to 12 weeks

54. Homework
1. Explain how FSH and LH influence maternal physiology and the embryo development?
2. Describe the development of the Placenta and the fetal membranes (Chorion and Amnion)
3. Describe how to identify the gestational sac: include MSD.
4. Describe the blood flow in early pregnancy.
5. Describe how to identify the embryo and cardiac activity
6. Describe how to determine gestational age in the first trimester.
7. List and describe first trimester complications.
8. What are the risk factors for early pregnancy failure?
9. Describe the yolk-sac evaluation.
10. What are the risk factors that may increase the risk of spontaneous miscarriage?
11. Explain the usefulness of hCG levels in first trimester pregnancy?

55. 1. The normal gestational sac grows at the approximate rate of
1 mm per day
2 mm per day
1.5 cm per week
2.5 mm per week
2. The corpus luteum cyst of pregnancy is maintained throughout the first trimester by what process?
Production of luteinizing hormone by the anterior pituitary
Production of hCG by the Trophoblastic cells
Growth of the amnion
Differentiation of the embryonic disk

56. 3. A grown rump length measurement of 16mm corresponds to what gestational age?
7.6 weeks
58 days
Both a and b
Neither a nor b
4. A thin, echogenic circular structure is seen surrounding the embryo, separate from the secondary yolk sac. What does this represent?
Primary yolk sac
Chorionic membrane
Amniotic membrane
Decidua capsularis

57. 6. What is the typical Doppler waveform pattern for trophoblasic flow?
5. With endovaginal scanning, a small soft tissue mass is seen anterior to the abdominal wall of an 11 week embryo, at the location of the umbilical cord insertion. What is the probable explanation for this finding?
Early diagnosis of an omphalocele
Early diagnosis of a gastroschisis
Normal herniated bowel in the umbilical cord
Amniotic band syndrome causing evisceration
6. What is the typical Doppler waveform pattern for trophoblasic flow?
High velocity, high resistance
Low velocity, high resistance
High velocity, low resistance
Low velocity, low resistance

58. 7. A mean sac diameter is used to estimate gestational age under which of the following circumstances?
When an accurate CRL cannot be measured
Prior to visualization of the intracranial landmarks for BPD
If the sonographic findings suggest an anembryonic pregnancy
More than one of the above
8. The chorionic membrane is derived from what component of the conceptus?
Decidual capsularis
Trophoblasts
Chorionic villi
Decidua basalis

59. 10. In what part of the placenta does maternal blood circulate?
9. A normal yolk sac is first seen with endovaginal Sonography at approximately what gestational age?
5 weeks LMP
6 weeks LMP
5 weeks after conception
6 weeks after conception
10. In what part of the placenta does maternal blood circulate?
Chorionic villi
Marginal sinuses
Intervillous spaces
Chorion frondosum

60. 13. False placenta previa can be caused by
11. During the first trimester, the choroid plexus is seen filling the lateral ventricles.
True
False
12. The decidua that is associated with the implantation site in the endometrium is called
Decidua parietalis
Decidua capsularis
Decidua basalis
Decidua Vera
13. False placenta previa can be caused by
Over distended maternal bladder
Lower uterine contractions
Evaluation too early in gestation
All of the above