Ultrasonography During Pregnancy

Ultrasonography During Pregnancy. Dr. Bahaa El Mohamady M.D..

Sequence • Introduction to Obstetric Ultrasound • Technology • Common Uses • Types of USG • Indications of Ultrasound Examination • Application of Ultrasound in Trimesters • Fetal Age Estimation • Conclusion • Q & A session.

Obstetric ultrasonography , or prenatal ultrasound , is the use of medical ultrasonography in pregnancy , in which sound waves are used to create real-time visual images of the developing embryo or fetus in the uterus The procedure is a standard part of prenatal care in many countries, as it can provide a variety of information about the health of the mother, the timing and progress of the pregnancy, and the health and development of the embryo or fetus..

Indications Clinical Applications Obstetrical US Assessment of the Fetal Well- being Invasive Procedures Amniotic Fluid Volume CTG Biophysical Profile Doppler US.

The Definition of Ultrasound (1): The term "ultrasound" refers to sound waves of a frequency greater than that which the human ear can appreciate, namely frequencies greater than 20,000 cycles per second or Hertz (Hz). To obtain images of the pregnant or nonpregnant pelvis, frequencies of 2 to 10 million Hertlz (2 to 10 megahertz [MHz]) are typically required..

Ultrasound Sound waves of frequencies higher than the hearing limit of the human ear are called ultrasonic waves The limit is by convention 20 KHz Medical practice frequencies between 1-10 MHz are commonly used.

Technology : • Sound waves reflecting back from the fetus or image structure -Y displayed on the ultrasound screen Alternating current is applied to a transducer made of piezoelectric material -5 intermittent high frequency sound waves exceeding 20,000 cps are generated.

The transducer emits a pulse of sound waves that passes through the layer of soft tissue Interface between structures of different tissue densities Some of the energy is reflected back to the transducer A small electrical voltage Display on a screen Bone is dense (echogenic) white on the screen Fluid (anechoic) black Soft tissues -+ varying shade of gray.

Choice of equipment : Transabdominal scanning 21) + Transvaginal scanning Doppler and color flow imaging.

Safety : no confirmed biological effects in mammalian tissue have been demonstrated in the frequency range of medical ultrasound (AIUM, 1991).

Trans Vaginal Ultrasound (TVS) • Method of choice for — Monitoring infertility disorders — Diagnosis of ectopic pregnancy — Differentiation of normal and abnormal 1st trimester pregnancy — Diagnosis of congenital anomalies in trimester • Patient to have empty bladder because — Uterus will be pushed posteriorly out of the field of view of the transducer.

Trans Vaginal Ultrasound (TVS) cont • Specially designed high frequency transducers • Higher resolution images • Favorable for obese patients or in early stage of pregnancy • Limitations include — Reduced beam penetration — More invasive nature of the technique.

Components of basic ultrasound examination according to Trimester pregnancy 1st trimester Gestational sac location Embryo identification Crown rump length (CRL) + Fetal heart rate motion Fetal number •.0 Uterus & adnexal evaluation 2nd and 3rd trimester Fetal number Presentation Fetal heart motion Placental location Amniotic fluid volume Gestational age + Survey of fetal anatomy Evaluation for maternal pelvic mass.

Clinical Application of Ultrasound (2): 1. Diagnosis and Confirmation of Viability in Early Pregnancy The gestational sac can be visualized from as early as 4—5 weeks of gestation and the yolk sac at about 5 weeks. The embryo can be observed and measured at 5—6 weeks gestation. A visible heartbeat can be visualized by about 6 weeks. Transvaginal ultrasound plays a key role in diagnosing incomplete or missed abortion, when the fetus can be identified, but with an absent fetal heart and in a blighted ovum. vd Ultrasound sac showing yolk sac (ys) and Figure 6.3 embryo (e) with the vitelline duct (vd).

2. Determination of the Gestational Age and Assessment of Fetal Size and Growth Up to approximately 20 weeks gestation the range of values around the mean for measurements of fetal length, head size and long bone length is narrow and hence assessment of gestation based on these measures is accurate. The biparietal diameter (BPD) and femur length (FL) can be used to determine the gestational age. Measuring the fetal abdominal circumference (AC) and head circumference (HC) will allow assessment of the size and growth of the fetus, and will assist in the diagnosis and management of fetal growth restriction. The combination of these parameters can provide more accurate estimation of fetal weight than any of the parameters taken singly. Gestational age cannot be accurately calculated by ultrasound after 20 weeks gestation because of the wider range of normal values of AC and HC around the mean..

Figure 6.5 Biparietal diameter (BPD) Femur length (FL) Figure 6.6 circumference (AC) measurernent Figure 6.7 demonstrating the correct showing the stomach (S) and the umbilical vein (U) ; - In IUGR: if it is symmetrical, there will be low total growth rate. If it is asymmetrical, there will be asymmetry between head measures (BPD and HC) and AC "the head is bigger than the abdomen - In diabetic pregnancies, the abdomen is disproportionately bigger due to the effects of the (2) insulin on the fetal liver and fat stores.

5. Placental Localization At the 20 weeks scan, it is customary to identify women who have a low- lying placenta. At this stage, the lower uterine segment has not yet formed and most low-lying placentas will appear to 'migrate' upwards as the lower segment stretches in the late second and third trimesters. About 5 per cent of women have a low-lying placenta at 20 weeks will eventually be shown to have a placenta previa. The transvaginal approach is taken with caution. 6. Measurement of Cervical Length Evidence suggests that approximately 50 per cent of women who deliver before 34 weeks gestation will have a short cervix. The length of the cervix can be assessed using transvaginal scanning..

Ultrasound in Assessment of Fetal Well-being. 1. Amniotic Fluid Volume 2. Cardiotocograph (CTG) 3. Biophysical Profile 4. Doppler Investigation.

1. Amniotic Fluid Volume A reduction in amniotic fluid volume is referred to as 'oligohydramnios' and an excess is referred to as 'polyhydramnios'. The fetus has a role in the control of the volume of amniotic fluid. It swallows amniotic fluid, absorbs it in the gut and later excretes urine into the amniotic sac. Congenital abnormalities that impair the fetus's ability to swallow, for example anencephaly or oesophageal atresia, will result in an increase in amniotic fluid. Congenital abnormalities that result in a failure of urine production or passage, for example renal agenesis and posterior urethral valves, will result in reduced or absent amniotic fluid. Fetal growth restriction can be associated with reduced amniotic fluid because of reduced renal perfusion and hence urine output. Two ultrasound measurement approaches give an indication of amniotic fluid volume: Maximum vertical pool: less that 2 cm = oligohydramnios, greater than 8 cm = polyhydramnios. v/ Amniotic fluid index: in the third trimester, it should be between 10 and 25 cm; values below 10 cm indicate a reduced volume and those below 5 cm indicate oligohydramnios, while values above 25 cm indicate polyhydramnios..

2. Cardiotocograph (CTG) The cardiotocograph (CTG) is a continuous tracing of the fetal heart rate used to assess fetal well- being. Features which are reported from a CTG to define normality and identify abnormality and potential concern for fetal well-being include the: baseline rate, baseline variability, accelerations and decelerations. The recording is obtained with the pregnant woman positioned comfortably in a left lateral or semi-recumbent position to avoid compression of the maternal vena cava. An external ultrasound transducer for monitoring the fetal heart and a tocodynometer (stretch gauge) for recording uterine activity are secured overlying the uterus. Recordings are then made for at least 30 minutes with the output from the CTG machine producing two 'lines', one a tracing of fetal heart rate and a second a tracing of uterine activity..

4. Doppler Investigation The use of Doppler ultrasound allows the assessment of the velocity of blood within fetal and placental vessels and provides indirect assessment of fetal and placental condition. Waveforms can be obtained from both the umbilical and fetal vessels. Umbilical artery: Waveforms obtained from the umbilical artery provide information on placental resistance to blood flow and hence indirectly placenta 'health' and function. An infarcted placenta secondary to maternal hypertension, for example, will have increased resistance to flow. Fetal vessels: Falling oxygen levels in the fetus result in a redistribution of blood flow to protect the brain, heart and adrenal glands, and vasoconstriction in all other vessels. The middle cerebral artery will show increasing diastolic flow as hypoxia increases, while a rising resistance in the fetal aorta reflects compensatory vasoconstriction in the fetal body. Absent diastolic flow in the fetal aorta implies fetal acidaemia. When late diastolic flow is absent in the ductus venosus delivery should be considered as fetal death is imminent. Measurement of velocity of blood in the middle cerebral artery also gives an indicator of the presence of fetal anaemia. The peak systolic velocity increases in this situation. This technique is particularly useful in the assessment of the severity of Rhesus disease and twin-to-twin transfusion syndrome which results in anaemia in the donor twin..

Ultrasound and Invasive Procedures (2): Ultrasound is used to guide invasive diagnostic procedures such as amniocentesis, chorion villus sampling and cordocentesis, and therapeutic procedures such as the insertion of fetal bladder shunts or chest drains. If fetoscopy is performed, the endoscope is inserted under ultrasound guidance..

Evaluation of ultrasound to determine gestational age Crown Rump Length Biparietal diameter • Femur Length Head Circumference Abdominal Circumference (CRL) (BPD) (FL).

Should First Trimester US be routine? Determination of EDD Optimise the time for fetal anomaly scan Enhance performance of serum screening test H/O ectopic pregnancy/miscarriage Intrauterine / ongoing pregnancy Diagnosed early unanticipated miscarriage Better informed when to deliver which complication arise in second or third trimester Minimise false positive IOL for postmaturity Multiple pregnancy and chorioamniocity can be determined.

Problems of early pregnancy • Miscarriage • Ectopic pregnancy Abdominal pregnancy Trophoblastic disease Ovarian probs in early pregnancy Uterine fibroids Pregnancy with II-JCD.

Diagnostic Signs of Early Pregnancy Failure in the First Trimester V MSD of equal to or greater than 25 mm without an embryo V Crown-Rump length of equal to or greater than 7 mm without cardiac activity V Absence of embryo with heartbeat at 2 or more weeks after an ultrasound that showed a gestational sac without a yolk sac V Absence of embryo with heartbeat at 11 days or more after an ultrasound that showed a gestational sac with a yolk sac.

3D &4D Ultrasound. 3D ultrasound refers specifically to the volume rendering of ultrasound data. When involving a series of 3D volumes collected over time, it can also be referred to as 4D ultrasound 3D ultrasound is useful, among other things, for facilitating the characterization of some congenital defects, such as skeletal anomalies and heart issues. With real-time 3D ultrasound, the fetuse can be examined in real-time..

Examples of ultrasound in fetal congenital malformations screening.

NUCHAL TRANSLUCENCY (NT) • 11 to 14 wks • 3 mm • Abnormal NT may indicates: — 1. chromosamal abnormality • Trisomy 21 or 18 or 13 • Turners Syndrome — Cardiac abnormality — Prediction ofTTTS (4 fold increase in risk).

Example of early pregnancy problems diagnosed by ultrasound.

Hints about some basic ultrasound procedures.

Biparietal diameter BPD. bpd.

Abdominal Circumference. GROWTH MEASUREMENTS. UV.

Abdominal Circumference. AC anatomy.

Femur Length. FL 26 weeks.

Oligohydramnios. Reduced Liquor vol. MPD < 3 cm up to 36 weeks MPD < 2 cm 36 weeks - term.

Polyhydramnios. polyhydram. MPD > 8 cm.

Minor placenta praevia. Partial & marginal praevia.

Major placenta praevia. Plac praevia. Plac praevia.

Fundal placenta. normal plac + Doppler.

Summary of ultrasound obstetrics indications.

INDICATIONS FOR FIRST-TRIMESTER ULTRASOUND EXAMINATION.

INDICATIONS FOR SECOND- AND THIRD-TRIMESTER ULTRASOUND EXAMINATION.