Uteroplacental and luteal circulation in normal first-trimester pregnancies: Doppler ultrasonographic and morphologic study

Intervillous circulation in all three trimesters of normal pregnancy assessed by color Doppler

Our cross-sectional study included 115 healthy pregnant women in gestational age between 7 and 24 weeks. The aim of the study was to compare resistance (RI) and pulsatility (PI) indices, peak systolic velocity (PSV), end-diastolic velocity, and temporal averaged maximum velocity (TAMV) of the spiral arteries and vessels within the intervillous space in all three trimesters of pregnancy. The impedance to blood flow within the intervillous space significantly decreased towards the mid-pregnancy (p < 0.01) and then remained stable. Blood flow velocities within the intervillous space expressed by PSV, EDV and TAMV increased significantly (p < 0.01) towards the mid-pregnancy. After reaching the plateau between 16 and 22 weeks of gestation, these parameters remained almost constant until the 36th gestational week. Near the term low-significant decrease of blood flow velocities was noted: for PSV and TAMV p < 0.07, and for EDV p < 0.05. A significant increase in continuous intervillous blood flow velocity was noted from the 11th week onward (28 +/- 12 vs. 36 +/- 12) until the 36th week of gestation (36 +/- 12 cm/s). The first report of the haemodynamic changes within the intervillous space during pregnancy may have implication in better understanding of the metabolical interchange between maternal and fetal side.

Histological study of decidual spiral arteries and the presence of maternal erythrocytes in the intervillous space during the first trimester of normal human pregnancy

During the first trimester in normal human pregnancy, endovascular trophoblast migrate along the decidual spiral arteries and invade their walls to produce physiological change. There is controversy as to whether invading trophoblast plug the arteries and prevent blood flow into the intervillous space. Using light microscopy, placental bed sections from 25 first trimester gravid hysterectomy specimens were examined. From each specimen, one section was divided into equal central and peripheral compartments. Maternal red blood cells were present in the intervillous space in all specimens, in both central and peripheral areas. In total, 232 decidual spiral arteries were found, each of those represented by several cross sections, 136 in the central area and 96 in the periphery. Seventy-nine per cent had undergone physiological change (significantly more in the centre than in the periphery), 63 per cent contained scattered endovascular trophoblast, 20 per cent had plugs of trophoblast partially occluding the vessel and 17 per cent had plugs totally filling the vessel lumen. These data confirm that in the first trimester of normal pregnancy, maternal blood enters the intervillous space, total plugging of the arterial system by trophoblast is not common, and more spiral arteries undergo physiological change in the centre than in the periphery.

Variations in expression of copper/zinc superoxide dismutase in villous trophoblast of the human placenta with gestational age

This study investigated expression of the key antioxidant enzyme copper/zinc superoxide dismutase in the villous trophoblast of the human placenta at different gestational ages from 8 weeks (last menstrual period) to term. Immunostaining for the enzyme was observed in the cytotrophoblast cells at all stages. Staining was generally absent from the syncytiotrophoblast at 8 weeks, except for small isolated areas close to the basal surface. The size and location of these areas suggested they were the result of recent cytotrophoblastic fusion. By 10 weeks, examples were more frequent and diffuse staining throughout most of the syncytiotrophoblast was observed at 12 weeks. The intensity of the immunostaining within the syncytiotrophoblast continued to increase until 14 weeks, by which time it matched generally that within the cytotrophoblast cells. A similar pattern of staining was observed within term material. These results are entirely consistent with the hypothesis that the oxygen tension within the intervillous space is low throughout the first trimester of pregnancy. They support the idea that an effective maternal circulation to the human placenta is only established at the start of the second trimester.

Maternal circulation in the first-trimester human placenta--myth or reality?

The classic theory of development of the uteroplacental and intervillous circulation determined that maternal blood enters the intervillous space in high-pressure streams from the early first trimester. This theory has recently been challenged and our hypothesis to be presented is that the intervillous circulation is not fully established until the end of the first trimester. Ex vivo studies of hysterectomy specimens have demonstrated that trophoblastic plugs obstruct blood flow into the intervillous space in early pregnancy and only at 12 to 13 weeks do these plugs become loose and allow for continuous maternal blood flow into the intervillous space. This concept is supported by many other experimental findings. In complicated early pregnancies the uteroplacental circulation demonstrates flow characteristics that are strikingly different from those of normal early pregnancies. In abnormal pregnancies increased flow within the intervillous space is demonstrated by color Doppler imaging. Our hypothesis supports other studies that have shown that the embryo favors an environment low in oxygen during early development and that oxygen levels in placental tissue are low in the early first trimester. The classic drawing of placental circulations is based on second- and third-trimester studies, and its applicability to the early first trimester should be revisited because we will show that new data support the hypothesis that the development of the early intervillous circulation is a progressive phenomenon.

Conflicting data on intervillous circulation in early pregnancy

According to classic embryological textbooks intervillous circulation is established early in the first trimester. This process starts with trophoblastic invasion of the decidua in which proteolytic enzymes facilitate the penetration and erosion of the adjacent maternal capillaries with formation of the lacunae. After the lacunar or previllous stage trophoblast invades deeper portions of endometrium with belonging spiral arteries. This gradual process finishes with direct opening of the spiral arteries in the intervillous space under the fully developed placenta. This classic concept of establishment of the intervillous circulation was challenged in 1987 and 1988 by the experiments of HUSTIN and SHAAPS. The authors believed that blood flow in the intervillous space is absent in incompletely development before 12 weeks of gestation. After the introduction of the new generation of far more sensitive color Doppler devices in the last few years, our group and several others reported a positive finding of intervillous circulation during the first trimester of pregnancy.

Ultrasound contrast media and their use in obstetrics and gynecology

Contrast media have gained acceptance to enhance ultrasonography in many fields of medicine; in particular, cardiology. Several agents have been described and many more are being manufactured and tested. By increasing the number of strong sound scatterers, these agents improve images by increasing the amount of echoes. This is true both for grey-scale and color or Doppler imaging. Their use in obstetrics is very limited at the moment because of safety issues. In a laboratory setup, they have been shown to markedly enhance placental imaging. In gynecology, imaging of the uterine cavity and Fallopian tubes is greatly improved. A potential area where ultrasound contrast may find a role is gynecological oncology. Vascularity is increased in many tumors, but usually vessel diameter is small and velocity low. One can therefore expect future use of the ultrasound contrast agents in ovarian or other gynecological neoplasms.