Berdasarkan berat badan rujukan menurut Departemen Kesehatan, bayi yang lahir dengan gizi baik akan mempunyai berat badan antara 2,5 kg sampai 3,4 kg. Pertambahan berat badan bayi sangatlah pesat, tetapi laju pertambahan berat badan makin lama makin berkurang. Pada umur 5 bulan, berat badan bayi menjadi dua kali berat lahir, sedangkan pada umur 1 tahun beratnya tiga kali berat lahir, dan pada umur 2 tahun berat badannya menjadi empat kali berat lahir. Tujuan penelitian adalah untuk mengetahui hubungan antara berat badan lahir terhadap pertambahan berat badan usia 12 bulan pada bayi yang di lahirkan di klinik bidan praktek mandiri (BPM) di Kota Lubuklinggu Propinsi Sumatera Selatan Tahun 2019, sampel sebanyak 108. Desain penelitian cross sectional. Hasil penelitian menunjukkan 81,5% bayi lahir dengan berat badan ≥3000gram, sebanyak 47,2% bayi yang mengalami kenaikan berat badan 3 kali berat lahir, 47,2 % bayi diberi ASI eksklusif, 63% bayi mendapat MP ASI pada usia ≥ 6 bulan, 59,3% bayi menderita penyakit infeksi, 88% ibu yang memiliki usia kehamilan ≥ 38 minggu, 70,4 % ibu yang memiliki pendidikan ≥ SLTA, 63% bayi rutin melakukan penimbangan berat badan serta 80,6% bayi mendapatan imunisasi lengkap. Terdapat hubungan antara berat badan lahir (p value = 0,001) dan status imunisasi (p value = 0,017) terhadap pertambahan berat badan bayi pada usia 12 bulan. Perlu adanya peningkatan program antenatal care (ANC) dan peningkatan program cakupan imunisasi/universal child immunization (UCI) serta peningkatan kunjungan posyandu agar bayi dapat mencapai berat badan yang ideal pada usia 12 bulan.

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Based on the reference weight according to the Ministry of Health, babies born with good
nutrition will have a weight between 2.5 kg to 3.4 kg. Baby's weight gain is very rapid, but the rate of weight gain decreases over time. At the age of 5 months, the babys weight is twice the birth weight, while at the age of 1 year it weighs three times the birth weight, and at the age of 2 years the weight becomes four times the birth weight. The purpose of the study was to determine the relationship between birth weight to weight gain of 12 months in infants born at independent practice midwife clinics (BPM) in Lubuklinggu City, South Sumatra Province in 2019, a sample of 108. The study design was cross sectional. The results showed 81.5% of babies born with a weight of 0003000gram, as many as 47.2% of infants who gained weight 3 times birth weight, 47.2% of infants were given exclusive breastfeeding, 63% of infants received MP ASI at the age of ≥ 6 month, 59.3% of babies suffer from infectious diseases, 88% of mothers who have gestational age ≥ 38 weeks, 70.4% of mothers who have education ≥ SLTA, 63% of babies routinely weigh weight and 80.6% of babies get complete immunization . There is a relationship between birth weight (p value = 0.001) and immunization status (p value = 0.017) on infant weight gain at 12 months of age. There needs to be an antenatal care (ANC) improvement program and an increase in the universal child immunization (UCI) program and an increase in posyandu visits so that babies can achieve the ideal body weight at 12 months of age.