Back pain in the fourth month of pregnancy is very common, but this situation is not normal. At this time, the patient may be due to physiological factors leading to back pain, may also be due to pathological factors onset, for example, the patient at this time may be due to lumbar muscle fatigue, followed by back pain, this time the fetus is in the period of rapid development, its weight in a short period of time may be rapid increase. Therefore, pregnant women may overuse their lumbar muscles in order to maintain balance when standing, which will cause lumbar muscle fatigue and lead to pain, at this time, pregnant women just need to lie down and rest for a period of time, which will be able to alleviate this situation. Pregnant women may also be due to the following pathological factors that lead to back pain: First, pregnant women may have osteoporosis, because the rapid growth and development of the fetus may cause the mother to produce relative malnutrition, followed by the onset of osteoporosis, it is easier to produce back pain. Secondly, sometimes it is still a symptom of preterm labor, for example, when the growth and development of the fetus is slowed down or the mother’s body is damaged, it is often manifested as a symptom of low back pain.