Objectives An ultrasound study to establish the nature and limits of fetal growth in a low risk population from 22 weeks of gestation until term. Design Prospective, longitudinal ultrasound study of 274 low risk pregnancies involving organised scanning schedules with all measurements performed by one observer using the same equipment.Results Growth velocity charts have been created for a number of ultrasound parameters including estimated fetal weight, by applying appropriate statistical methods to the serial data. The rates of growth of the biparietal diameter, femur length, abdominal area and estimated weight each have characteristic patterns demonstrating maximal growth rates at different gestations. Conclusions Appropriately derived and calculated ultrasound fetal growth velocity standards have been established. These data are suitable for the evaluation of ultrasonically estimated fetal growth rates in the prediction of adverse perinatal outcome and the further investigation of the role of the intrauterine environment in the origin of adult disease.been highlighted6. This study was designed to establish such standards of growth velocity for a number of fetal measurements in a low risk obstetric population. METHODSThree hundred and thirteen women attending the antenatal clinic at our hospital were enrolled into the study. Entry criteria were gestational age of less than 85 days confirmed by crown-rump length measurement and the absence of recognised risk factors for accelerated or retarded fetal growth (previous SGA or IUGR pregnancy, existing medical disorder or heavy smoking (> 20 cigarettes per day)). All the subjects were scanned for fetal anomaly at 18 weeks of gestation, which is routine practice in our department. Thereafter, the subjects were sequentially entered into one of the four scanning schedules (n = number continuing in the study). weeks (n = 67).These schedules gave weekly coverage of pregnancy from 22 weeks onwards. All ultrasound 60 0

Summary. The growth of total intrauterine, intra‐amniotic and placental volume during the latter half of pregnancy was studied longitudinally with ultrasound in 115 healthy women with normal singleton pregnancies. A parallel planimetric area method was used. The range and distribution of normal values between 20 and 40 weeks was determined for a main study group of 103 primiparous women with which values from 12 parous women were compared. Total intrauterine volume increased from a median of 1006 ml to 4420 ml, intra‐amniotic volume from 716 ml to 3406 ml and placental volume, calculated as the difference between total intrauterine and intra‐amniotic volume, increased from 259 ml to 801 ml. Variation between individuals was wide at all stages of pregnancy. No significant difference was found between primiparous and parous women. Between successive 5‐week periods from 20 to 40 weeks there was evidence that women tended to maintain their initial volume ranking. During the 30–35 week period, rate of growth of total intrauterine and intra‐amniotic volume was somewhat faster than the near constant mean rate at other times, while the rate of growth of placental volume decreased after 30 weeks towards term.

A comparison of a prolate ellipsoid method and a parallel planimetric area method for measuring volumes with ultrasound was made using phantom models of water-filled balloons scanned under set conditions. Correlation with actual volumes was significantly better with the parallel planimetric area method (p < 0.02) with 93.3% of parallel planimetric area measurements being within 5% of the actual volume compared with only 33.4% of measurements obtained with the prolate ellipsoid method. For The accuracy of volume measurements by both a parallel planimetric area method and a prolate ellipsoid method, applied to a structure similar in shape to that of a pregnant uterus, was assessed by a method in which the volumes of water-filled rubber balloons were determined under defined con& tions. MATERIALS AND METHODSThirty sets of measurements on thin walled rubber balloons were made. The shape of the balloons approximated a prolate ellipsoid and they were filled with varying but unknown amounts of water. Care was taken to express all air from the balloons which were then tied securely at the neck and placed in warm water until scanned to allow for equilibrium of inside and outside water temperatures.Scanning was conducted in a thermostatically controlled metal water tank. At a temperature of 47 2 3°C the velocity of sound in water is similar to the average velocity of sound in tissue (1540 m/sec).? Water temperature was kept as near to this value as possible and checked before and after each set of measurements. A correction factor for the velocity of sound in water was calculated when the water temperature was lower than 44°C. A rubber mat was placed on the bottom of the tank to increase scatter and reduce reverberation. The balloons were secured in the water bath