Table 5.

Articles published using AI to improve fetus face monitoring: objective, backbone methods, optimization, fetal age, and AI tasks

Study	Objective	Backbone Methods/Framework	Optimization/Extractor methods	Fetal age	AI tasks
Fetal facial standard plane (FFSP)
(Lei et al., 2014)	To address the issue of recognition of standard planes (i.e., axial, coronal and sagittal planes) in the fetal US image	SVM classifier	AdaBoost for detect region of interest, ROI) Dense Scale Invariant Feature Transform (DSIFT) Aggregating vectors for feature extraction fish vector (FV) Gaussian Mixture Model (GMM)	20 - 36 weeks	Classification
(Yu et al., 2016)	To automatically recognize the FFSP from US images	Deep convolutional networks (DCNN)	N/A	20 - 36 weeks	Classification
(Yu et al., 2018)	To automatically recognize FFSP via a deep convolutional neural network (DCNN) architecture	DCNN	t-Distributed Stochastic Neighbor Embedding (t-SNE)	20 - 36 weeks	Classification
(Lei et al., 2015)	To automatically recognize the fetal facial standard planes (FFSPs)	SVM classifier	Root scale invariant feature transform (RootSIFT) Gaussian mixture model (GMM) Fisher Vector (FV) Principal Component Analysis (PCA)	20 - 36 weeks	Classification
(Wang et al., 2021)	To automatically recognize and classify FFSPs	SVM classifier	Local Binary Pattern (LBP) Histogram of Oriented Gradient (HOG)	20 - 24 weeks	Classification
Face anatomical landmarks
(Singh et al., 2021a)	To detect position and orientation of facial region and landmarks	SFFD-Net (Samsung Fetal Face Detection Network) multi-class segmented	N/A	14 - 30 weeks	Miscellaneous
(Chen et al., 2020c)	To detect landmarks in 3D fetal facial US volumes	CNN Backbone Network	Region Proposal Network (RPN) Bounding-box regression	N/A	Miscellaneous
(Anjit and Rishidas, 2011)	To detect nasal bone for US of fetus	Back Propagation Neural Network (BPNN)	Discrete Cosine Transform (DCT) Daubechies D4 Wavelet transform	11 - 13 weeks	Miscellaneous
Facial expressions
(Dave and Nadiad, 2015)	To recognize facial expressions from 3D US	ANN	Histogram equalization Thresholding Morphing Sampling Clustering Local Binary Pattern (LBP) Minimum Redundancy and Maximum Relevance (MRMR)	N/A	Classification
(Miyagi et al., 2021)	To recognize fetal facial expressions that are considered as being related to the brain development of fetuses	CNN	N/A	19 - 38 weeks	Classification