Lactation is the instinct of almost all mammals, including human beings. With the development of human society, the function of lactation has gradually deviated from nature instinct. Breastfeeding related industries, such as milk bottles, formula and breast pumps, have formed a vast consumer market, leading to a transition from breastfeeding mothers' individual instinct to the social division of labor. Previous studies found that the incidence of lactational mastitis remains largely unchanged post World War II with some reporting an increase, suggesting the hazards of lactational mastitis still exist under the background of social division of labor. Breast milk contains ingredients that improve the immunity of newborns. By affecting mothers' breastfeeding, lactational mastitis pose a hazard for newborns, increasing the chances of developing respiratory and gastrointestinal diseases. For breastfeeding mothers, severe mastitis may develop into breast abscess due to improper treatment in the early stage. In addition to antibiotic treatment, incision, drainage and even surgery may be required. These potentially increase the risk of developing postpartum depression, type II diabetes, breast cancer and ovarian cancer. Compared with other mammals, humans and cows have a higher incidence of lactational mastitis, indicating that human intervention in breastfeeding may be the cause of the high incidence. On the other hand, as a result of walking upright, humans' hands are liberated, forming complex and diverse breastfeeding position. According to the Sakra World Hospital, these positions are classified into eight types: cradle, cross cradle, supine, football, Australian hold, inverted lateral, lateral cradle, and lateral. The pilot study demonstrated that different breastfeeding positions are closed related to the occurrence of lactational mastitis, and to the location of mastitis. Assuming that the baby's sucking factors remain the same, there must be differences in the milk drainage in different breastfeeding positions under the influence of gravity. Researchist speculate that breastfeeding women who opt to a position that cause an anti-gravitational expulsion of milk are more likely to develop lactational mastitis. Therefore, this study aims to investigate how the scientific guidance on the gravitationally assisted breastfeeding positions will reduce the occurrence of mastitis.

Time of recruitment: 1 December 2021 - 30 April 2022. Two thousand women who meet the following criteria are to be recruited:(1) primparious women; (2) full-term delivery;(3) age ≤35 (4) breastfeeding within 7 days after delivery; (5) with autonomous behavior ability; (6) provide voluntary informed consent; (7) ability to breastfeed individually(8) prenatal breast ultrasound shows no breast lesions.. Exclusive criteria: (1) abnormal breast or nipple development (Poland syndrome or degree II and above inverted nipple); (2) history of breast surgery; (3) history of chest radiotherapy; (4) history of malignant tumors; (5) History of mastitis; (6) severe cardiovascular and cerebrovascular diseases, chronic diseases (Ecog score >3, long-term medication affects breastfeeding); (7) skin diseases or connective tissue diseases; (8) Hepatitis, syphilis, gonorrhea, AIDS and other infectious diseases. Criteria of elimination after recruitment: (1) failure to follow the breastfeeding instruction; (2) painless breast mass.

Participants are to be randomly divided into the interventional group which provides guidance on gravitationally assisted breastfeeding, and into the control group which provides general breastfeeding guidance. Through the social media network WeChat, each participant receives breastfeeding guidance before their first breastfeeding, and once a month until 6 months after childbirth. Additionally, at 3 and 6 postpartum, the breasts will be examined by a breast surgeon at Shenyang Women and Infants Hospital. Infant's height and weight will be measured and recorded at 6 months. The incidence of breastfeeding mastitis and the rate of baby weight gain are compared between the groups. This clinical cohort study aims to investigate effects of scientific guidance on the gravitationally assisted breastfeeding positions on the occurrence of breast mastitis.

Inclusion Criteria:

• primparious women;
• full-term delivery;
• age ≤35;
• breastfeeding within 7 days after delivery;
• with autonomous behavior ability;
• provide voluntary informed consent; • ability to breastfeed individually;
• prenatal breast ultrasound shows no breast lesions.

Exclusion Criteria:

• abnormal breast or nipple development (Poland syndrome or degree II and above inverted nipple);
• istory of breast surgery;
• history of chest radiotherapy;
• history of malignant tumors;
• history of mastitis;
• severe cardiovascular and cerebrovascular diseases, chronic diseases (Ecog score >3, long-term medication affects breastfeeding);
• skin diseases or connective tissue diseases;
• Hepatitis, syphilis, gonorrhea, AIDS and other infectious diseases.

• primparious women;
• full-term delivery;
• age ≤35;
• breastfeeding within 7 days after delivery;
• with autonomous behavior ability;
• provide voluntary informed consent;
• ability to breastfeed individually;
• prenatal breast ultrasound shows no breast lesions.