The pulse oximetry enables us to determine the degree of oxygen saturation both noninvasively and continuously by measuring pulsating wave absorbance in the peripheral tissues, such as fingertips. Some researchers have reported that the oxygen dynamics can be measured over the course of delivery using a pulse oximetry probe applied transvaginally to the fetal head.1–3 Moreover, the intravaginal optical probe for tissue oximetry using the near-infrared spectroscopy (NIRS) has been developed.4,5 However, the sensor volume of (diameter 1 cm, length 5 cm) was too large to apply during delivery. The dimensions of the commercially available small optical probes for the brain (NIRO-200NX, Hamamatsu Photonics, Hamamatsu, Japan) and the muscle (Hb-14, ASTEM, Kawasaki, Japan) were (width, length, and thickness). The sensors’ volume of was too large for monitoring the fetus directly. Additionally, the significantly low data capturing rate is one of the biggest drawbacks to these procedures. East et al. have reported that during the active phase of labor, every method has a significant rate of signal loss and the loss of sensor contact occurred up to 64% of time with oximetry.6 Another drawback of this transvaginal procedure is that the probe often moves away from the fetal head during delivery, which may lead to an intrauterine infection caused by rupture of the gestational sac. Furthermore, these methods are essentially invasive, as the probe is inserted into the uterine cervix only after the rupture of the gestational sac. In addition to these problems, many patients feel discomforted by the intravaginal sensor. Obstetricians also feel that there is interference with the cervical examination by the sensor. Although many clinical trials of the fetal pulse oximetry have been performed, its clinical usefulness has been controversial. Thus, there are no established methods for detecting the fetal hypoxia during parturition yet. At present, many obstetricians look forward to further improvement of oximetry and a better understanding of clinical management.